I can totally relate to your sentiments. When I first started playing Warframe, the grind felt like it was near impossible, especially with my limited gaming time. But I think its because the game isn't designed like a traditional game. Much like MagPrime explained, the game is essentially designed to be "everlasting", with content and loot being continuously added over time. As where in traditional games, there's a starting point and a set endgame(no more content to be added). Warframe doesn't have an endgame, only future content/loot. So it needs to balance loot drop rates and content release as to retain its audience. Then there is also the marketing aspect with platinum and trading. After all DE is a company with employees and servers to pay to keep running.