It is not, so far as I know, an "extra network." It's one of many types of instance on the fediverse. Many of them have features that do not perfectly interoperate with others. The more popular ones eventually get to be widely supported as things evolve. Mastodon is not the standard, it's just one among many.

Also, you're a lemmy user. It's one of the worst when it comes to interoperating smoothly with the rest of the network.