The approach that you mention has its limitations, and what many (most?) editors do is quite a bit more complex than that. For example, I don't want a new LSP

The approach that you mention has its limitations, and what many (most?) editors do is quite a bit more complex than that. For example, I don't want a new LSP instance for each file, I want to re-use the same LSP instance if files belong to the same project. For this, my editor needs to understand which directory is the root of the project, and this varies per-language. In case of neovim, there's a nvim-lspconfig plugin that ships all this configuration and lots of other little nuances. I guess the folks from VSCode preferred lots of little plugins instead of a single big one.