CGNAT is standard on mobile connections, it's more common than getting your own IPv4 address. Over the last few years, it's becoming increasingly common for residential connections, because ISPs can no longer get additional IPs for free from their regional numbering registry.
It's now cheaper for ISPs to deploy CGNAT than to purchase new IP blocks. Since IPv4 is provided for legacy compatibility, performance is not a priority.
> users' modem/router combos, and those are pretty fast and reliable
What? No, most of the infrastructure you see deployed at users home is trash. Majority of people don't buy their own network gear to replace the ISP gear they receive when signing up and ISP skimps on the costs of hardware for customers.
