Boiling it down to 3 things:
- Content Scale & Variety - Lemmy has a lot of content but it's very tech/political heavy. It doesn't have much to offer outside of that domain. Meanwhile, there's a whole shitposting subreddit dedicated to an NFL conference -- I don't even closely follow professional American football, but it's glorious.
- User Experience Friction - You can't just sign up, you need to pick a server. You've already lost a significant amount of people in that step.
- User Base - There's nice folks on here, but some really sour the experience for the rest of us by being straight up hostile if we don't agree on every little detail.