Because as @Paulie_D states above, they have different built-in modifications. Sensors, communication array and they ofcourse do offer a little protection against physical harm. Even though they were not perfect in every aspect, they seem to help in a variety of situations, following this conversation from Episode VII:
UNDER THE GRATING
Finn pulls the grating over them as Rey works on the controls.
REY: You think this'll work on the Stormtroopers?
FINN: Yeah. Their masks filter out smoke, not toxins.