I brought up CGNAT because my American ISP does use CGNAT. We are now paying an extra monthly fee for a static IP, which I believe is the only option they have for getting a public IP (i.e. no intermediate fee amount for a public non-static IP).
It might be more fair to say that most American residential ISPs don't have to do that because they have access to giant legacy IPv4 allocations. Comcast alone has 65 million IPv4 addresses, for example (including a /8, /9, and /10 and several /11s).
I think they could make more money using CGNAT and leasing those IPs out to data centers. Also another comment in this thread mentions that their cellular plan sold as a residential internet connection doesn't use CGNAT, but their phone plan from the same company does..
Maybe! CGNAT isn't free, of course, you need pretty beefy machines to handle ISP numbers of clients. So, is the capex for the machines, engineering time to set them up, and opex for keeping them running more or less than they'd make back from leasing their net blocks? Hard to say.
