And if I put a web URL into my telnet client I just get a bunch of raw HTTP! Not everything on the internet is part of the web. There have always been other protocols: IMAP/SMTP for email, IRC for chat, NNTP for newsgroups, XMPP for instant messaging, and RSS for subscriptions.
The idea that everything has to be done over the web is what’s really undermined “the idea of HTML as a markup language”. If HTML is a markup language, why would you use it for all these other use cases, most of which were handled with much better performance on hardware from twenty years ago?