The problem is NAT solved the same problem more easily and cheaply. It was at the cost of making it difficult for every host to talk directly to every other host, but it turned out most of the people building networks didn't want that feature anyway.

We already ran out of ipv4 about 15 years AGO.

64 bits would be enough to avoid run out, but hierarchical allocation would still be a problem. 128 bits is long enough for many levels of hierarchy. (And yes, you can subnet all the bits, not just the first 64)