I see your point, but I think you're missing the broader picture here. Web protocols are not just used because they are there, but because the stack is very elegantly layered and extensible, well understood and tested, and offer strong security guarantees. It's not like encryption hasn't been tacked onto HTTP retroactively, but at least that happened using proper staples instead of a bunch of duct tape and hope as with other protocols.

All of that isn't really important, though. What makes a major point for using HTTP w/ TLS as a transport layer is the ecosystem and tooling around it. You'll get authorization protocols like OIDC, client certificate authentication, connection resumption and migration, caching, metadata fields, and much more, out of the box.