I was hanging out in the IPv6 mailing lists at the time the various solutions were being debated.
The prevailing attitude was "the Internet is about to die from routing overload without IPv6, so we can stick whatever complexity we want inside it, and they will have no choice but to accept it."
Except that new router hardware and new incremental software improvements came out, and the enormous complexity of the "boil the ocean" redesign inherent in IPv6 was rightly regarded as completely unnecessary.
If the IETF had simply made IPV6 "ipv4 with longer addresses", (and there was a proposal to do just that), implementations and deployment would have been dramatically simpler and would have stood a real chance of succeeding.
Instead we have this baroque construction, which I _still_ have to explicitly disable in my work environment because various bits of supposedly IPV6 software don't play nice together.