Hah! I think I’ve spent about 500 hours in Rimworld and haven’t come close to the endgame. I’ve never gotten any of the spaceship parts or anything like that.
I've played Rimworld since the Kickstarter beta. Back in the old days, it was possible to finish the space ship over the weekend. I guess the game has also crept much larger and added more filler.
I played it quite early too (I don't remember if I kickstarted , it or bought it after, but it was long before it was on Steam). Yes, it has become much larger, but its not filler, in my opinion, because the additional content adds additional depth and nuance to the game, characters and the story that unfolds. Much of it can also be ignored, if you so wish, because its based around content that you can construct (eg if you want to ignore the alcohol system, then don't grow hops and brew beer). I suppose you could call that filler, but it exists because if you do want to make use of it, its systems integrate with the games other systems and create interesting stories as it gives the characters more depth.
You're probably right though, I suppose it also made the game much harder to "complete" compared to the early days.
Rimworld tries its best to be a drama generator, but unfortunately doesn't do a good job at it. A lot of the additions for the drama side added little actual "depth" and more on "breadth". For example, factions, family relationships, and cleanliness are more tedious than fun. You don't really go "OMG, that's hilarious", you go "Oh come on why'd you have to kill your daughter?"
I think is the big problem with many AAA games these days is that breadth (more unnecessary features) is a lot easier than adding depth.
Compare with Dwarf Fortress, where you can make a mermaid bone farming industry, reservoirs, magma powered river thawing system, waterfall dining rooms, or a magma powered waste disposal system.