If every instance is isolated on its own domain with no gateway between them, I don’t see much point to the fediverse.

I only really want to touch upon this point, but the Fediverse platforms were originally designed as a return to the old forum-style format of communities, where you have your own little cozy corners of the internet, with your own rules and culture, while also being decentralised and resistant to the problems of centralisation.

The fediverse, however, allows you to reach outside of your own community and follow/socialise with people inside other communities seamlessly (which, in truth, it does do), negating the need of everyone having to make accounts and identities on every single site/community they come across.

The concept of having the fediverse just be thousands upon thousands of instances seamlessly all connected to each other for maximum content discoverability is only really a mindset that has occurred recently after Musk's acquisition of Twitter, and attention was put on Mastodon. Before this, people just resided in their own little communities and talked to people they knew rather than specifically looking for more people.

The developers of these platforms are looking into what they can do regarding this, but they don't want to stray far from the principles of these software platforms by making them into social media sites that are just clones of the social media sites they're trying to move away from.