Buying v4 addresses isn’t sustainable and drives the prices up long term.
CGNAT v4 at scale requires hefty and expensive translation boxes that have to keep growing with traffic volume.
Native v6 immediately takes the majority of your traffic - most of the big CDNs & content providers like Netflix support v6 already.
I wonder why they're not then. Clearly it's not a very big incentive.
Regardless of if an ISP offers IPv6 or not, they still need IPv4. Thus if you are small and/or have enough IPv4 address space, IPv6 is just an additional cost and burden.
The support burden of IPv6 isn’t trivial when you do not control the end user devices.
IPv6 bandwidth isn’t cheaper nor more performant. From a business perspective, the only thing you get from IPv6 is a larger address space and a smaller need for (CG)NAT.
There is an incentive to deploy IPv6 if your (CG)NAT costs and/or the costs to acquire more IPv4 addresses is larger than the costs to deploy and support IPv6.
The tipping point is different for each ISP.
It also depends on the regulator environment whether you are forced to deploy IPv6 or not.
Larger ISPs tend to be longer lived and often have large pools of v4 allocations that they didn't pay market rates for, so are happy to sweat long term.