Maybe they shouldn't have used http:// for something that isn't http.
Nah, users are too dumb and "my precious adoption rates"
Nah, users are too dumb and "my precious adoption rates"
General consensus in marketing seems to be that people can't memorize anything more than domain names, and maybe also a "www." or a single word path behind the domain - but the scheme seems to be universally seen as "technical cruft that non-technical users can't be expected to deal with". (with the one exception that "http:// = bad and https:// = good")
So I guess companies don't want a situations in which they suddenly have to teach their users that, no, it's not "awesomecorp.com", it's actually "https3://awesomecorp.com" (but NOT https://3awesomecorp.com, that's a scammer) etc etc
It's especially important with HTTP/3 because there are network environments where HTTP/3 doesn't work and so you need to fall back to HTTP/2, and you obviously want that to work seamlessly.
In addition, the basic security structure in the Web is the origin, defined in RFC 6454, and origins are defined by a triplet of [scheme, host, port]. It would not be good to have HTTP over TLS and HTTP/3 be different origins. For instance, you don't want to lose all your cookies if the site turns HTTP/3 on or off.