@HopelessDemigod An age old question! I think the core answer is "lack of customer demand", networks are there to provide services to their customers in exchange for money. IPv6 is rarely a "big ticket feature" (side story: I know when I worked at Cloudflare that we forced many ISPs to establish IPv6 peering/support in order to have CF PoPs in their network)

My suspicion is that as time goes on, IPv4 performance will get more crummy as more and more CGNAT is added, and at that point adding IPv6 support to your content (aka websites) is a obvious pick. The eyeball side will add IPv6 to take the load off their expensive CGNAT boxes.

"We" are seeing some of this playing out already, But 90,000+ different networks have to do it before it makes sense, and many of those networks are not growing and so see no pressure to deploy CGNAT, and thus IPv6.