The artificial resource constraints created by IPv4 are a substantial barrier to entry. Prediction: we’re going to see a court case that forces a mandatory retirement of IPv4 sometime in the next 15 years.
Remember the IE6 banners? There will be a time in ten years (haha it's always ten years!) when you'll see "Our site runs with degraded performance over IPv4. Please contact your administrator."
It also makes it much more difficult for customers to stress your upload bandwidth though.
For whom? There are lots of providers (for example Huawei) that offer turnkey solutions for ISPs to painlessly roll out CGNAT.
The current situation is that the ISP can lessen load on their CGNAT solutions by providing IP6.