It’s stateful. Specifically, if a plain router stops working, BGP will route around it, and all you did was drop packets. If NAT stops working, you don’t just

It’s stateful. Specifically, if a plain router stops working, BGP will route around it, and all you did was drop packets. If NAT stops working, you don’t just drop packets, you drop whole connections. Applications don’t tend to tolerate dropped connections as well as they tolerate dropped packets.