except that for high performance networking, storing stuff in normal RAM is simply not an option if you want to keep an acceptable throughput. (>40gbit). One would need to store NAT state in some sort of TCAM/CAM table.
Guess what, having a 175 gigabyte of (T)CAM is drastically more expensive.
Guess what, having a 175 gigabyte of (T)CAM is drastically more expensive.