In theory I guess. But you’d need a ton of funding just to get the server power for that, and there’s no guarantee that users will switch over to your service. And if Bluesky starts turning bad then they could start blocking your instance. Also the users are much more valuable than the data. There’s lots of ways this could fail to pan out. The Fediverse is much more flexible to new instances joining.

maybe it would be simple to fork this source code and form your own community

The network effect makes this extremely difficult, even with the source code, it’s basically starting from scratch again.