Because we grew up internalizing external expectations. You have to unlearn that if you don't want to feel pressured into completing the last three achievements, but that's hard AF especially for people who are masking a lot. And until then you feel guilty for not completing a game because you missed an achievement or didn't find all collectibles.
There's only one achievement of the ones left that I actually care about and I haven't gotten around to attempting it yet. I've mostly been playing modded levels and doing any% speedruns.
All I can say is I'm glad I figured myself out before playing this game. I think I'd have missed a lot otherwise. Still haven't finished Core, but working on it...
Ah I remember that game. Was extremely hard for me. I ended up cheating to beat it. Just hooked in cheat engine to grant invincibility and unlimited jumps, because I got way too frustrated.