One of the things I love about lsp-mode is how it automatically installs any language server I need, when I need it.
I would rather install one package and be done, than use one built-in package, and have to manually hunt, download, and manually maintain language-servers for all the different languages I'm using in my programs, on all the machines I do programming on.
If eglot wants to become the defacto standard, it will need to solve this sooner rather than later.
But I suspect RMS will be opposed to having Emacs automatically download "non-free" (not GPLed) code?