what’s the benefits of using Lemmy compared to the others? I found this picture on Google.

It does not.

Negative, to force that would oppose the goals of open source. Now if someone wanted to develop a one size fits all Fediverse platform there's nothing stopping them.

No but they could all run on a single domain. For example I'm on lemmy.blahaj.zone but blahaj.zone is primarily a calckey (like Mastodon but less minimalist than Mastodon) instance.

admins could roll deployments that are tightly integrated if they wanted now, just takes time to setup. I think most servers are dealing with the basics right now.