I became a mod for a tv show subreddit just because nobody was posting weekly episode discussion threads, and I wanted to post those threads because I personally enjoy them. I don’t care about all the other stuff (removing posts/comments/etc). I’ve modded for another tv show so that I could literally just make it prettier (better design for the top banner, more readable sidebar etc.) So the motivation in both cases was really about improving my own experience as a user. In a smooth-running subreddit it’s not a lot of work.

However, what happens is one mod can go kinda nuts and if they are one of the top mods there’s no way to rein them in. I was part of a group of 10 mods on one of those subs and 9/10 were reasonable, but the 10th was wayyyyyy too invested - worked on the sub something like 16 hours a day (I think they were on disability?), wanted to personally approve every post, got really really upset if people didn’t follow the sub’s rules, took it all very personally, banned a ton of users, just way way too invested in “his” subreddit and in making it exactly the way he wanted it. He was one of the top mods so the rest of us couldn’t do anything.