Quic has been around long enough that I suspect it's simply a common policy for both tcp and udp on 443. If you just want to charge for access, rate limiting is easier and there is almost never any local person involved in managing it.

A lot of VPN blocking isn't a specific, deliberate policy choice by the network owner, it comes in from default policy options on whatever awful vendor they use. The people seriously concerned about outgoing tunnels providing access back into protected networks that hides from normal packet inspection are a different case.