I don't think you can frame it as "adverse ISPs". I mean in some respects yes, but also IPv6 made the assumption that networks want to be shallow & wide, yet th

I don't think you can frame it as "adverse ISPs". I mean in some respects yes, but also IPv6 made the assumption that networks want to be shallow & wide, yet that's not where we've ended up. Rather, we now tend to have a lot of depth to the routing tree. Is this because of NATs? Possibly. But also network isolation turned out to be a powerful tool. And every step of isolation is necessarily another subnet. So now the depth of IPv6 is a limiting factor. Great you can have infinitely wide networks, but you can't expect to nest them much anymore. And that's a rather big limitation.