If you’re in the US, it’s because all of the major ISPs siphoned up much of the ipv4 address space so they can still offer it to everyone.
In Australia, on the other hand, most ISPs provide CGNAT by default, although most of them offer a free opt-out and have ipv6. Mobile services are also typically CGNAT, although many offer ipv6 + 464XLAT (an ipv4 compatibility mode using ipv6).
In developing countries some sort of ipv6 solution is almost universal, particularly those with higher populations such as India, since it would cost an absurd amount of money to buy up that amount of ipv4 address space today.