If there is any risk you should wear protection?
If thats the case you should wear nomex 24/7 Because there is always some risk.
In combat it makes sense, you are getting fired at. In other military flight ops they are preparing you for combat, so again it makes sense.
In civilian flight ops the chances of being in a post crash fire, while possible, are about the same as you being involved in a post crash fire in your automobile. Do you wear nomex when going to get the groceries?
Safety science teaches you to mitigate the greatest hazard. There comes a point where the increased fatigue created by fire resistant clothing exceeds the mitigating value of the protection it affords.
It should be up to the pilot to determine where that point is. We dont need babysitters.