HSTS was created specifically to prevent the MITM from downgrading HTTPS to HTTP.

As for MITM blocking a protocol, that is a noticeable situation, and one that does not give the attacker any control over the cryptography used on sensitive data. A downgrade attack is very different from blocking a protocol. The user doesn't notice, and the attacker gains some control over the cryptography used.

In the end, what sense does it make to have a TLS version an attacker can opt out of? All you get is defence against passive MitM. Until we aren't safe against those passive MitM with TLS 1.2 it makes no sense to rush TLS 1.3. Especially because that rush would really hurt when it turns our TLS 1.2 is insecure, at which point the rushed solution becomes vulnerable to all active MitM attacks.

Now consider, what level of access to infrastructure only allows for passive MitM?