> IPv6 has failed at being better, being accessible, or both.

I don't agree that it has. IPv6 is clearly better (no collisions between address space and thus no NAT requirement), and it's perfectly accessible to anyone who actually tries. I'm not by any means a top tier network guy but even to me IPv6 is dead easy to setup. The problem with the v6 transition is that people have very inaccurate views on one or both of those points (usually they falsely believe NAT provides security benefits, or they falsely believe IPv6 is a difficult thing to implement). I'm not sure how to fix this widespread misinformation but that is the problem from what I've seen.

IPv6 primarily solves a problem that most people either don't have ("I have IPv4 IPs already") or don't care about ("I don't know/care what my IP is") and it introduces a bunch of problems people didn't have before like worries over comparability with existing hardware/software (improving all the time) or even just "now I have to spend a bunch of time learning about how to correctly and securely implement this on my network" (still a problem)

Maybe one day in the distant future, IPv4 collisions/shortages will be an actual problem for most people. If that happens, those people will naturally make the switch. Until then, why would they?

It turns out a bunch of people actually like NAT. They like it so much that they pushed for solutions like NAT66 so that they can keep it even after switching to IPv6.

If IPv6 offered substantially better security/privacy, speeds, reliability, or introduced some new killer feature people didn't even know they wanted until they learned about it there wouldn't be any reason to try to force people to move to v6. Because it doesn't do any of that, and most people are happy with IPv4, they'll stick with what has been working for them.

Even 15 years ago IPv6 was much worse than IPv4 for most of the people. Only when the mobile operators has started to insist on it then the usage started to grow to significant numbers. Which showed the real problem with IPv6: lack of compatibility with IPv4. That was absolutely possible 30 years ago, but the designers decided that it would just complicate things.