The problem is that adding so many bits to IPv6 addresses, by way of intended integration of the EUI / MAC address in particular is not actually necessary and is a bit of a mistake. As a rule, no one even wants their MAC address propagated across the entire Internet, nor to be registered in DNS either.

There are some technical advantages to doing things that way of course, but they are arguably rather outweighed by the administrative disadvantages. The protocol could have been designed so that typical layer 3 addresses were not much longer, nor harder to type or remember than IPv4 addresses are.

IPv6 having 128-bit is a huge advantage for transition. NAT64 shoves the 32-bit IPv4 address into the host field.

MAP-T shoves the source and destination IPv4 addresses and ports into IPv6 address. This makes IPv4-IPv6-IPv4 NAT possible. Which means it is possible to run IPv6-only network with IPv4 at on the customer network and edges.

There are certainly advantages as you point out, but just because you have 128 bit addresses does not mean it is convenient for 64 bits of that to be filled with semi-random data.