The main reason that a lot of veterans still play this game is for the events which have leaderboards that you can compete for.
Leaderboards are a way for a clan to show their passion for that game, they show how dedicated players can be to a single event, whether its an event where you have to do a lot of missions in order to achieve a high score or an event where you have to do an endurance run to get to the top. In past events, players have invested nearly 20 hours without breaks just trying to get to the top because its something that will be on record forever that everyone will see. Seeing your friends, clanmates and Clan wherever they may be on those leaderboards after the event is over is a memory that we can look back on and remember how much we enjoyed the grind; the compromises we had to make and the challenges we had to overcome in order to get the best possible run in.
There are very few leaderboards in this game that are set in stone after a period of time and these Operations and Events give everyone a chance to strive towards putting their name as high up on that list as they can so other people can see the tremendous amount of effort that they put in.
There are *so* many competitive clans out there, many clans have recently been rising and preparing specifically for this event and with all of the new players that have just come in for PoE, they won't get to experience the event environment where everyone is trying out a new mission type or gamemode and experimenting with warframe setups trying to find niche combos to later share with your clan in order to boost them up as high as possible.
In my opinion, taking away these leaderboards is a bad decision, at the end of the day, it is what it is but I sincerely hope that in the future we will either see leaderboards for new event as well as the past events returning with a chance to change those 0's on our profiles into all sorts of numbers :D