One could have created a library which conformed to some specification, written the library a single time, then compiled it for different platforms. Editors could then have loaded that shared library and used it just as they wrote in support for a language server. There's no need to get a network server involved.

You still have the majority of development effort in the library, instead of individual text editors. You still have the joy of a nearly pure piece of code, without OS-specific paradigms like networking which impede progress. You still have a simple interface with the editor.

I see exactly zero benefits of having a language server over a traditional shared library, except with a network server you make a trade off where you gain latency and other networking problems, and you gain absolutely nothing.

I don't even know of any central language servers, which were one of the core benefits of the LSP design. "ooh we can all share a language server which is kept up to date independently of our editors! squeeee!" Where's that? Why is that a benefit at all? Presumably you'd still need to shut it down to update it, and someone has to manage it.

The experience that people using editors got when aeditor developers started thinking about how to do something better is what the users love, not the LSP itself. LSP triggered this change in thinking, but anything could have, and I'm honestly surprised that nothing else did prior to LSP.