We don't "know better" as such. The issue is that the Nissan Engineer has to work within the constraints of the laws as they exist. EGR being a case in point.
It is essentially only there as an anti-pollution measure but the trade off is that the engine "swallows" a whole heap of contaminents etc at the cost of accelerated wear and performance. Indeed that is why EGR is blocked by the ECU and Engine management at higher engine loads
Blocking the EGR is great for the engine but terrible for the environment.