You're right, consumer devices could be easily NATed, and I've heard rumors that ISPs in some parts of the world actually do it. But it's notoriously difficult

You're right, consumer devices could be easily NATed, and I've heard rumors that ISPs in some parts of the world actually do it. But it's notoriously difficult to set up NAT on a large scale without seriously impacting performance, so large ISPs in the developed world tend to avoid it.