I have my opinion on this subject but I warn you this may be long a bit and the grammar would be mediocre at best so forgive me that, my native language is not the english.
Before I start I think it is important to describe what content creator we talk about and who is content creator.
Short answer - content creator is that person, whom creating a subject related to a topic which could be in game or outside of the game ( in this case ).
We can count as content creators the video makers because they also put energy into making videos which is consists the planning, making raw material, cutting the material and fine tune into a usable video which entertain or teach others. I do not know so much youtuber for warframe because I am also not bothers with them in the reality, but their existence is not weightless. The first and foremost reason why DE partnering with these content creators is they promoting the game and their subscribers giving them a potential playerbase. More or less the content creators changing each other so one leave other coming to fill the place but that is important for the game to have promoter otherwise less player can get into the game or won't know it at all. Of course not all subscriber will try the game but a x % possibly could go for it, and also y % could follow their youtubers so they leave the game also. Normally a company can promote their game via marketing but beign a medium sized semi independent game studio which use free to play model that is really matter, how many partner they have because paying small fees for partners is much cheaper than keeping a full marketing company which eats thousands of millions for promoting the game. Basically these youtube-twitch-mixer etc platform promoters are promoting the game with less money. In the old times before the internet was a thing or was not popular as today most of the companies if wanted to be successful needed to spend tons of money to promote their wares.
Less promoter nowaday means potentially less player because some will follow their promoters while others not mind if leave or stay regardless of creator we talk about. Not all potential subcriber will be player but a good portion could be and some marketing for a game is always good which normally should have spent millions on it. Comparing to Destiny in the activision era they spent a lot of money on marketing, which meant the game was not profitable because the huge creation cost and marketing cost made the game too expensive with high exceptations. In Warframe the thing is the opposite, because DE in my best knowledge " could be wrong, pls keep in mind that " they does not spent millions on marketing and what money they saved pumped into the game what they do nowadays too. Their only major flaw is their content creation speed and quality is not always the best. They have a bad habit to make half baked content and that is not really good for the promoters whom specialized to make warframe contents because if there is bothing to show then they cannot earn money.
In this point we need to separate content creators, because those whom making warframe art-concepts, skins and other stuff are widely different and they are also playing the game but they have their in game products which makes them a fix source of profit. In the other hand the video content makers need to make weekly at least one video about the game but if you have no idea what to do just running in circles then you could often stress yourself what to do which feels fresh and not repetitive. Burn out in this case could be the stress, because making content, redoing content and focusing on making content bearing with critics can be stressful. Also if they forced to play the game, then the moral also differ than if you just log in and play for fun. They are often in the wrong end, where they cannot enjoy the game, because they need to do some content which is not repetitive, unique enough to show the possible new players how good warframe is. Normally if there is no content players searching for other games or habits so they can stay long in the game. I personally never make breaks, just plays less and I still have something to do. Honestly those whom stay in a long time in a game, they do for passion and because they like what the game can contribute.
Most of the video content creators burn out of this reason, and that is important to have a stabile content creator base with high numbers of subscribers and it matters to DE also, because that is not less important how many players these peoples can grant. A content creator with 10k sub is less important than a creator who have 150k or 200k because if we see in percents a 10k sub base could possibly be all but 10% maximum who will plays the game for long time and that 10% with higher numbers means more player who could spend on the game. Normally I would agree with those whom say this is unfair to those whom not popular and just playing the game and the creators has granted rights and advantages but their symbiotic link is based on only the possible player generating. A player like me, who just plays the game, plays the game since the open beta start, spent money on the game in my early 1-2 year then stopped spending because they changed the login system and that meant no discounts anymore for me so no sees benefit to spend money on them anymore is not that important, than a player who could bring new faces here. The loyality and the passion and love towards to the game is not enough to keep them well fed so it is normal they will instead promote these promoters because they basically make their duty so they don't need to do that.
If we talk about the non video content creators, their existence is less important, because they creating fan arts and maybe skins and weapons which possibly could be sold in game, but that is still means less profit to the developers than a video promotion. The best promotion to the devs would be if they hire more person, who helps the make a lot and good quality content and the game could sells itself by the quality but we know the reality is different. A good product not always mean fix everything and still you can bankrupt no matter how good your product if you cannot share with the majority. Warframe is quite popular game, but yet needs to grow root in epic, discord, other gaming platforms and make a bit more expensive marketing to be recognized as a popular fun game. The only problem is the game indeed fun at the early times but if there is no meaningful content for the old timers, whom probably burn out or finished all major content in normal space, then the game getting negative reviews which impacts the sales aswell. In 2 part need they imporve a lot, fixing old content so they could balance the game around it, and the new and old player retaining. Both thing possible to do, but the latter is harder because they need a clear direction what the game needs so they could balance it.
Fixing old content needs a direction, what they should buff, nerf, what mechanics needs to be refreshed and what needs to be rid out.
Personally I am caring on how many player could plays the game, because the more is always better, better because you can find friends, refresh your passion, or just teach new ones how to play. Content creators also needs to make the game more popular so we cannot say they don't missing if they are leaving, because in this situation the devs needs them, because of their lack of own power for marketing. Companies like EA can make a huge marketing and they don't depend on promoters, because no matter how bad ther image, they still can find x million vegetables whom buying their products 🙂. Their marketing power is higher because they started as publisher and they developed a strong marketing team which can sell everything to everyone. Different companios operate differently and DE is that company, which is more dependant on the free marketing sources than the own marketing power. Maybe the Leyou helps them with this, because that is important to them too, that the game thrive and remain successful, otherwise not worth to invest the time and rescources on DE.
This is just my opinion, and feel free to critize or agreeing with me.