From what I understand about the providers, they really don't like it when you're generating outbound traffic. Sure it's advertised to be symmetrical, but the actual hardware they place here can get bogged down if you start hosting a popular site (or seeding too much).
And of course, if they can charge you for a static IP then defaulting to dynamic is imperative, isn't it? Pretty sure they'd try that with IPv6 too just to keep the income stream.
Regardless, the actual issue with IPv6 around here seems to be that the providers either don't know how to or don't care to implement it properly. Sure I can tick on "IPv6" in my router, but that doesn't mean I have an unbroken chain or routing hardware that supports it connecting me to the great internet.
Mordor itself, Russia. Technically, most ISPs support IPv6 here but as I said each has something weird in config that makes using it... Fun. I don't remember specifics since I'm mostly looking at it from consumer side, but I could try finding the article (in russian) that talked about it.
My current connection doesn't have IPv6 at all according to https://ipv6-test.com/, although I'm not 100% if it's because of provider or Cisco AnyConnect blocking shit.
When you when you sign up for internet here, you get a dynamic IP, it's been that way for... As long as I can remember, really. Definitely more than ten years. I know in Moscow people used to get white IPs way back when, but that's long gone. Not really a problem since most people don't host anything.