Can't home routers, much like they all now have NTP by default, just have a firewall installed that by default blocks all incoming traffic unless it's a respons

Can't home routers, much like they all now have NTP by default, just have a firewall installed that by default blocks all incoming traffic unless it's a response to outgoing traffic? So, no prefix translation, everything has a real IP, and all incoming traffic still gets dropped on the floor by default.