After like 1K hours of play, I realized Warframe is extremely... LOOPY.
I mean, the whole game (or like 98% of it) revolves around this LOOP: "Play to earn stuff to make more powerful weapons/frames, so you can play higher level missions and get more arcane stuff to get even more powerful weapons/frames"... and on and on and on... forever.
The gameplay itself is great and fun, but it's practically always the same: same missions on different places, same enemies... and on and on and on. There's no goal, just this eternal LOOP (maybe it has to do with... "eternalism"? LOL!).
Apart from running around in this LOOP, everything you do is pointless: the enemies are always there, the bosses come back to life, "Operator, the System needs you": and it always will (because this LOOP keeps the game running).
Most players never "enjoy" the game, they run as fast as they can to mission end, to get their stuff. They're like gerbils in their LOOPY rotating cage: running as fast as possible and getting nowhere. ;-)
Sure, one could play differently: going slow and stealthy, solving Spy puzzles for the sake of it... but why doing it, when the missions are always the same, and you already did them a hundred times? WF is a bit like the "Groundhog Day" movie: stuck in a LOOP of a never-ending carnage :-D
I don't have a solution. I come back every now and then, for a new weapon or frame, and because running around and killing aliens in WF is basically FUN... for a while. Then the sense of DEJA VU comes back again, and I ask myself: "Why am I doing this?". :-)