I wouldn’t call what reddit is doing “thriving”. The experience of what used to make Reddit, Reddit (the deep focused communities) is already quite decayed and has been decaying for some time.
Curate your Lemmy communities better and make an effort to interact as much as possible. Lemmy always feels super dead if you don’t actively look for new communities and instances to subscribe to, because the Fediverse is inherently in a changing state of flux of where the activity is. Lemmy does not auto populate your feed with a bunch of algorithm crap, you have to MAKE it show you what you want. I’ve built up a nice list of 40+ subbed communities and see lots of content.