Honest question: What am I actually playing for?

Title. For context, I've played Warframe when it first released as a kid and didn't understand anything, so now I've given it a fair shot now that I am older and can actually appreciate the game, I am mastery rank 9 now. I have cleared all the main quests so far and cleared all the junctions to my knowledge. I know this is not all the content in the game but to me so far it seems like this was the most obvious goal to work towards.

This is not a hatepost, far from it. I have massively enjoyed the story main quests so far. I like the world of Warframe, and the general gameplay loop is enjoyable. But usually in games like these, I always feel like there is a clear endgame that I am working towards which makes grinding worth it.

I come from games like Path of Exile 2 and Elder Scrolls online, and by no means are these games directly comparable, elements do carry over, especially the build homebrewing. In these games you also make your character strong to eventually beat the pinnacle content like massive bosses, or like in MMORPG's, big raids and trials, like group dungeon bosses etc.

So from playing, I've felt like just creating a massively overpowered build is kind of the thing most people strive towards, especially to challenge yourself with the steel path missions.

There's for sure a lot of things and content I have no idea about so treat this more as a: "What are you playing for?" inquiry type of post.

TLDR: I love the game so far but I don't really know what I am playing for, especially to make grinding feel worth it.