Sure, if there were a magic wand we could wave then it'd be great. Instead someone has to spend years implementing these features. Implementing a good editor is surprisingly hard work; it could easily take a team of developers multiple years to write a new one. To make it an excellent editor would take years longer.
Instead we have addons like Edit with Emacs (https://addons.mozilla.org/en-US/firefox/addon/edit-with-ema...). At once point there was an addon that swapped Firefox's normal editor for a GTK widget that wrapped all of emacs, but it was a bit janky and I haven't used it in a decade or more. I'm not even sure it would still work.