Comment by GuB-42

QUIC is actually a level 4 protocol, on the same level as UDP and TCP, it could work on IP directly, making it QUIC/IP.

They chose to keep the UDP layer because of its minimal overhead over raw IP and for better adoption and anti-ossification reasons, but conceptually, forget about UDP, QUIC is a TCP replacement that happens to be built on top of UDP.

Now for the answers:

- Why not HTTP over UDP? UDP is an unreliable protocol unsuitable for HTTP. HTTP by itself cannot deal with packet loss, among other things.

- Why not keep HTTP/2? HTTP/2 is designed to work with TCP and work around some of its limitations, it could probably work over QUIC too, but you would lose most of the advantages of QUIC

- Why not got back to HTTP/1? I could turn out to be a better choice than HTTP/2, but it is not a drop-in replacement either, and you would lose all the intersting features introduced since HTTP/2