[nvarsj]

Don't forget the history of TCP. TCP's congestion avoidance is the evolution of 20 years of managing large scale networks. Many papers later and the CA algorithms of TCP have been proven to work at large scale for a variety of traffic types. The internet as we know it simply wouldn't work without massive adoption of TCP. Even QUIC looks very similar to TCP, and is just an evolution of it in many ways.

It's a hard distributed problem: how do you coordinate many independent flows of traffic to efficiently utilise the many network links in the internet? Do this wrong at scale, and even broadband internet will feel like you're on a 2G mobile network.

Also I don't think it makes sense for HTTP to be on UDP. While it's stateless, you still can't tolerate packet loss with HTTP. Otherwise you'll try loading a page and maybe nothing comes back, or only part of it comes back. What then?