IP reputation is a tough problem with a lot of establishment behind v4. Even if they were to build up v6 reputation, since v6 addresses are cheaper, wouldn't they have lower rep?
The "reputation" concept has to be applied to network blocks in IPv6, because of privacy addresses, and they very clearly aren't doing that for whatever reason. I get at least one captcha a day from a stock Android phone that's been connecting from the same damn /64 for almost a whole year.
But there are way more /64s than /32s. They could apply it to /32s in ipv6, but then customers would share rep unless ISPs lease out /32s instead. Unfortunately gotta pay to play.
