This whole discussion was about what should have been done differently at the start of the IPv6 rollout to help it complete in less than a lifetime, not about the situation some decades in.
But that's what I mean: lots of ISPs have supported IPv6 for 1-2 decades. Most hardware & software already supported it a decade ago, and nobody should be using anything that old without updates. The only reason for an ISP today to not provide it is incompetence.
Two decades ago I was a member of a ISP consumer group, and we discussed it with a couple ISPs back then. They all were working on a planning for it (one smaller ISP even already implemented it back then!). Apparently in other countries ISPs were allowed to behave irresponsibly.
Really, the only way to force such incompetent ISPs out is if governments get involved, or if all/most backbone providers and IX operators set a date where IPv4 will become very expensive, and then one where it will be switched off...
