IPv6 is faster and more reliable because the user can connect to your site natively instead of going through NAT and CGNAT.
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.
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.