I joined because Reddit has become a cesspool of bots and toxic behaviour. Lemmy is still completely open-sourced, while Reddit isn’t at all now. Also, when you first sign up on Reddit currently, you get completely ignored now and can’t post or comment on regular subs.
For me, it’s mainly due to the global enshittification of the social networks I was using.
Lemmy is my first try with a fediverse network and I have to admit I love it. After only a few days of use my feed is so good that I already deleted Reddit :')
And also, the fact that Lemmy is not controlled by a single authority makes it even more satisfying to use.