Also, in some countries ISP's need to map the use of a specific ip address to a specific subscriber for law enforcment purposes. GCNAT is no exception to this and creates a large amount of overhead because the public IPV4 prefix space is shared between multiple customers.
But it’s a solved problem with mature solutions, decades old. Is it really financially expensive?
For instance, most Core/Edge routers (my experience is mainly with juniper MX series, but i assume the model is roughly the same for other vendors), you need specific licenses or interface card's to do stateful services like NAT.
Compared to doing IPv6, which is "just forwarding packets" and doesn't require the hardware to track state in nearly the same manner.
Most serious core/edge hardware vendors also do not put IPv6 behind licenses compared to CGNAT and other NAT-like features, because packet based forwarding is the most basic functionality a router should provide.
Routers which are able to do less state, also are frequently far less expensive.
So ipv6 support might be saving you costs already in a dual stack setting.
Until there is a bunch of exclusive v6 stuff customers will be up in arms over missing, the answer of which thing to prioritize is obvious.
Also, one of the reasons to do satellite internet is lower latency which is a bit hurt by CGNAT infrastructure.
Last, generally brand new ISPs are in the situation that they have a hard time of getting ipv4 address space. The incumbents, especially the older ones, were around when ipv4 addesses were still plenty so they usually have way less problems with ipv4 address space. Starlink only has 166k ipv4 addresses according to https://ipinfo.io/AS14593 . Compare this to AT&T which has over a hundred million for their AS 7018 https://ipinfo.io/AS7018 alone, and there are other AS numbers they have like AS20057 with 7 million ipv4s. This roughly matches the number of AT&T customers while Starlink has more than double the number of subscribers than its number of public IPs, with growth ahead.
And v6 connections help drop the pressure on NAT resources - and sites that are optimizing for mobile connections are already going to be on IPv6 where possible (due to mobile networks prioritizing v6 traffic for various reasons, including licensing - and NAT resource costs)