Are you sure? My experience so far has shown that only dnscrypt is widely supported.
Nevertheless, surely they must had some kind of issue with the existing solutions when they started working on it.
As for DNS over QUIC, I was under the impression that said solution did not make use of HTTP.
I believe it's possible to do both direct DNS over QUIC and ((DNS over HTTPS) over QUIC).
https://android-developers.googleblog.com/2018/04/dns-over-t...