It’s a different model.

Mastodon, like Twitter, is a person-centered setup. You can use hashtags, but most people don’t. You follow people not communities. As a result it’s basically microblogs, where most people are just posting into the void. Celebrities are followed more, so they get more replies, so there are more conversations. But, fundamentally it’s not really inviting interactions.

Lemmy, like Reddit, is a topic-centered setup. It has a bunch of communities and people post something because they think it might be interesting for people who are also interested in that community. Every post is basically an invitation to have a discussion about something.

I think the friction to posting something on Lemmy is slightly higher, but when you do, it’s more likely to generate comments.