the IPv6 addresses may be easier to get, but since they are pretty close to useless why would anyone accept one instead of an address that looks to the rest of the Internet like it's IPv4 (either NAT444, NAT464, or just NAT44 like ISPs are using today). NAT64 + DNS64 are a possibility, but they are both bigger unknowns than the other NAT options, and a large number of consumer devices will not work on IPv6, so those customers can't use NAT64.