This is mainly due to mobile devices only being issued ipv6 addresses by the telco 4g networks. They are the only ones using ipv6 on the millions of clients scale.
Comcast/Xfinity implemented v6 on their residential cable network 14 years ago ( https://corporate.comcast.com/comcast-voices/ipv6-deployment...)
Most other large eyeball networks have as well.
My current home ISP and my last one both support IPv6 just fine. It is not a mobile-only thing.