Of course someone else could just try to make a competing protocol with LSP, but I think that's a waste of time when it could most likely be incrementally and backwards compatibly improved quite a lot. And also, any given party only is one side of the equation, so any given entity only has so much sway here.
Exactly. And if "everybody" (except MS) in the committee agrees on the implementation of LSP, they can define a new common protocol too. The old LSP clients and servers won't stop working, they may slowly die out if the new protocol "wins".
Don't get me wrong, this is just a hypothetically perfect solution, which didn't happen before LSP and I'm sceptical that it will happen in the foreseeable future, as LSP is "good enough". And with "it" I mean that there won't be such a commitee, much less a new, common protocol.
It will always need a new, better and open protocol implemented in a successful editor or IDE to gain traction and spread (like what happened with VS Code and LSP).
Starting over with a new protocol, and replacing implementations for all the existing editors and languages would be a tremendous amount of work for relatively little benefit.
And either forking lsp, or creating a new protocol would cause fragmentation.
Also, VSCode is popular enough that even if the other editors forked LSP and made significant improvements, if VSCode wasn't on board, it would be a tough sell to get many languages and existing LSP implementations to adopt it.