"let them use IPv6!" -Marie Antoinette a/k/a your ISP that hasn't even rolled it out yet.
Why? Because for residential user that want low latency internet & low packet drop (CGNAT increase both), ISP can charge "business price" for dedicated IPv4 that aren't behind CGNAT. With IPv6, CGNAT is not needed.
Considering ISP/Telco in here is very scummy (they even perform MITM to inject ads, use Class 0 message / AMBER Alert for ads, etc.) I won't be surprised if that's the only reason why they didn't rolled out IPv6.