To me, it was the astounding amount of interactivity between the community.
At first I thought this was temporarily caused by the whole migration from the R site. But, just out of curiosity, I signed up to Mastodon and have enjoyed myself just as much as here.
Most of the Lemmy post's / Mastodon toots have almost as much or more comments / boosts than upvotes or favorites. It feels so organic and makes me realize how much these huge companies employ technics to pretty much force to interact the way they see fit.
It reminds me of that good old saying "you are not immune to propaganda", well I guess neither I nor anyone is immune to psychological tricks either.
P.S. I also love the fact that since there isn't pretty much any money involved, most opinions and interactions are genuine. Like, who is gonna pay this dude to advertise a book through BookWyrm? That increases immensely the odds that said person is being honest with their opinion of that book. It's amazing.
I completely disagree with that it works better for mastodon than lemmy. I think it was confusing as hell on mastodon, but makes perfectly good sense on lemmy.
Communities are a major advantage, because they allow people without technical knowhow and capital, to create and moderate places of common discussion. This was an issue with mastodon because instances was the only way to divide users into topics, which prevented non tech savvy people from making these categories. Having communities, separates the concern of hosting from the concern of moderating.
Furthermore, I don't understand the problem people have with "duplicate" instances. What is the issue with subscribing to more than one? It's not like you have a limited number of subscriptions. There are already a couple threads on the issue tracker on GitHub, about implementing "multi communities" and so on, it has too many downfalls in my opinion.