That’s Mastodon’s fault. The thing is that the comments are essential to lemmy. That’s why they are reposted. It’s just that Mastodon doesn’t implement groups well.

Because that was deemed the best way to let every subscriber of a community see all comments.

You misunderstood me. It’s not that the content is not relevant. It’s that the threaded discussion style just doesn’t map to Mastodon. Technically they can talk to each other but practically there is no sensible way to display the info on Mastodon.

The activitypub protocol that powers the fediverse is very versatile. So versatile that not every message can sensibly be displayed by every implementation.

Example: Mastodon does not support downvotes, lemmy and peertube do. In lemmy the descussion belongs to a group entity, in Mastodon everything belongs to a person entity.

Both are valid implementations of the spec but they use different parts of it that are relevant for them.

Not every message the activitypub can send is suitable for every platform. Reddit style discussions just don’t map to Mastodon.

The most important thing is that lemmy, Mbin, piefed, etc. can communicate freely. You can try to build a platform that does it all but I think it will be messy.