As someone that got introduced to it in 1996, and was a fan of XEmacs variant, still remembers enough keybindings and Elisp, supported beyond plain syntax highlighting was very much hit and miss, even nowadays.

But the effort to do so was then entirely duplicated for other editors. LSP turns an N*M effort into an N+M effort, the upshot of which being far more complete coverage for both editors and languages.

If the old emacs approach is so much better, why is emacs switching to using LSP?

I have been an emacs user for over a decade now, and if you think that language “support” was as good before LSP, I have a bridge to sell you.