It's a classic tragedy of the commons problem. Everyone has an incentive to delay doing anything for as long as possible, even though collectively we would all be better off if something was done.
The big mistake is to think that people will do the right thing because it would be better for everyone. That never works. The other big mistake is to think of the internet as a single thing. As well as being a series of tubes, it's also a collection of organizations and individuals who each have their own agenda.
We need some kind of effective carrot or stick to make the individual organizations do the right thing. It could be a government mandate. It could be a feature that you only get if you make your network IPv6 capable.
I almost wonder if it's too late, though. NAT may have won the battle by default. Another poster here said that as soon as blocks of IPv4 addresses start getting major cash value, change will have become impossible-- the same way patent reform is impossible.