One of the foremost obstacles to wide adoption is that IPv4 still works great and it's ubiquitous. There is no advantage or up-side to deprecating or abandoning IPv4 support at all. The only result of disabling IPv4 is a denial of service to a certain sector of customers or clients.

The only way this will change is by increasing pressure on the resource of IPv4 networks. It was a few years ago that AWS broke the news to me that I'd be paying for IPv4 addresses but IPv6 would remain free. If enough services are forced, financially, to abandon an IPv4 presence, then their clients would be likewise forced to adopt IPv6 in order to retain connectivity.

But with the ubiquity of CGNAT and other technologies, it seems unrealistic that IPv4 will become so rare that it becomes prohibitively expensive, or must be widely abandoned. So that availability of the legacy protocol will inhibit widespread adoption and transitions to IPv6.