IDEs have LSP support because they have a plugin that connects to an LSP server. The plugin is a very small piece of code compared to the language server. Creating a new client is not reinventing the wheel. In fact the entire philosophy of LSP is: one server to many different clients.

CLIs can also have a small piece of code that connects to an LSP server. I don’t see why IDEs should be the sole beneficiary of LSP just because they were the first clients imagined by the LSP creators.