That's intentional: they need you and your data tied to the server to make money. But there's no reason why it couldn't be local first (except the business model), since the bulk of execution is local.

Incidentally, I think that's why local-first didn't take off yet: it's difficult to monetize and it's almost impossible to monetize to the extent of server-based or server-less. If your application code is completely local, software producers are back to copy-protection schemes. If your data is completely local, you can migrate it to another app easily, which is good for the user but bad for the companies. It would be great to have more smaller companies embracing local-first instead of tech behemoths monopolizing resources, but I don't see an easy transition to that state of things.