I don't see how on-path devices could distinguish between DNS-over-HTTPS and DNS-over-TLS, provided they were run on the same port. It's just an encrypted socke

I don't see how on-path devices could distinguish between DNS-over-HTTPS and DNS-over-TLS, provided they were run on the same port. It's just an encrypted socketed connection. As for web apps... well, that's horrifying enough to be the real reason. Javascript should not be running its own DNS queries, outside of the system DNS settings - it's a layering violation that looks a lot like an end run around the "user agent" concept (i.e. the web app, rather than the browser itself, is the "trusted endpoint" and the user is considered an adversary). If web browsers actually wanted such functionality to be available, they could easily expose an API for it.