As someone who has done this while tired, it’s a lot easier to accidentally open extra ports to a publicly routable IP (or overbroad range of IPs) than it is to accidentally enable port forwarding or DMZ.

You could accidentally swap ips to one that had a port forward, some applications can ask routers to forward, etc etc. I donmt know how exactly we'd measure the various potential issues but they seem incredibly minor compared to the sheer amount of breakage created by widespread nat.