There’s Pixelfed which is a fediverse alternative to Instagram, but I don’t use it currently as I don’t share my photography online as LCP.
Peertube is a YouTube alternative but I’m not using that currently as well.
Other than them, there are other fediverse platforms that are basically Mastodon-like or Lemmy-like.
Things are fairly wonky right now, but I believe with time, effort and funding many if not all of the fediverse’s issues can be resolved.
Which Lemmy communities are you a part of that are currently tiny? I can lend a hand in posting/commenting there and keeping them active.
Ease of use.
With your one Discord account you join all the servers you care about and interact with online/IRL friends.
There are downsides that people at Lemmy will find dealbreaking and I absolutely agree with them, but the convenience of it being a chat, forum (almost), voice/video calling and gaming platform for free with (currently) no ads triumphs all of that for the majority of people, and that’s what makes it popular. It’s also cross-platform so no one’s left out.