CGNAT is also not cheap and very complex from a architectural point of view.

Vendors have been pushing it though, because implementing IPV6 only somehow is still a very, very scary thing for large ISP's to pull off.

what should happen is it should be very easy to deploy ipv6/4 translation mechanisms in ipv4 only networks, this would allow easy interopability and make it easier for the large networks to push IPV6.