the role of ISPs are not to act as your firewall. that's your routers job. NAT does nothing to increase that security realistically since most routers are close

the role of ISPs are not to act as your firewall. that's your routers job. NAT does nothing to increase that security realistically since most routers are closed by default to inbound connections. NAT as security is purely in the corporation realm of usefulness and afaik IP6 supports NAT just fine. it just wouldn't be a fundamental requirement for the internet to even exist.