You're wrong here. Folks actually deploying wanted better co-existence options for folks on IPv6, and it's shown up. You basically route ipv6 as IPv6 until you hit a network border that doesn't support IPv6, then go over to IPv4 for the rest. This let's me do IPv6 only devices without giving up IPv4.

As it is, they locked the upgrade cycle, because you can't do IPv6 only without losing access to IPv4 (historically).

In the end folks did get work arounds going using 464XLAT

https://datatracker.ietf.org/doc/html/rfc6877