The point is not needing a NAT translation table and running out of ports on your router.
My provider also delivers an IPv6 configuration with all ports closed. I can enable incoming traffic for the devices that need it.
Running out of ports is usually a misunderstanding, but a device doing stateful NAT will have a limit on how many states it can manage, and it's usually not fun when it goes over the limit.
I can't configure anything technical about my internet. Any change is paid, and often simply not possible.