I worked in this space for a while, in the US. Outside of the major cities, Internet service falls off extremely quickly. Like, shockingly so: you can be as close as fifty miles from, say Philly or Flagstaff and have zero fiber, zero cell coverage, just nothing.

The people who attempt to fill these gaps are commonly rural telephone companies, electric cooperatives, tribal entities, or mom and pop shops where the owner grew up on a Ditch Witch and only knows as much IP networking as essential to light up the fiber and get the packets flowing upstream.

They are enormously resource constrained in ways you might not expect, too, eg operations can grind to a halt because everyone is out with a chainsaw after a storm, or because the Guy that Knew Stuff about their network died suddenly.

They are very, very unlikely to decide to run an IPv6 network just because. There's no upside that makes the juice worth the squeeze for them.