Half of it is the sense of accomplishment people get from finally killing that white whale. The other half is wanting your accomplishments to feel special, and either consciously or reflexively gatekeeping to ensure they’re exclusive enough.

In romhacks specifically it’s also far more common to happen because in order to care enough to pull apart a game and really get into its guts, you’ve most likely played the original to death and know its intricacies backwards and forwards and so you want something that will engage you and people like you.

So you overtune it, only testing it on people with the same amount of game proficiency as you and your friends, who all find it tolerable because you’ve learned how to deal with the heat, whereas Joe Q Random will very likely have no idea that obviously Haste and Slow overwrite each other because they’re mutually contradictory statuses duh, etc etc.

If I made a romhack for FF5 for myself, as an example, I would be going in with esoteric knowledge like the fact that certain abilities pass on stat bonuses but others don’t, and I would tweak against John K Minmaxer instead of Joe Q Random. That would naturally make it harder and less casual-friendly.

Game design is HARD, yo.