I think the idea is that TCP over QUIC will be better than TCP over TCP, particularly since public wifi can have highly variable latency.
I would say they disable it deliberately to prevent VPN tunneling, its probably a sane decision to disable anything not needed for the intended purpose (or not putting effort in enabling it).
They are not sophisticated, they just do not want people leeching large amounts of data via the connection (which they basically perceive as http/1 or http/2).
Anyone using "something else" is basically noise.
For the most part it'll work no problem. Yeah tunnelling IP over UDP would be better, but ip over TCP is the only think you have... It's gonna work, as long as the underlying connection is stable enough.