In some cases, countries. In the country I'm thinking of (name omitted on purpose), you have an effective choice of two ISPs, both government-controlled.

Do they actually block/throttle all UDP?

What about encrypted TCP? Do they block/throttle everything but web and recognized traffic? If that's the case wrapping WG or ZeroTier or whatever in TCP would do nothing since it would still look like a weird unrecognized protocol with a max entropy (encrypted) data stream.