Current stethoscope designs utilize biauricular listening along with having a form factor that is often a hindrance in military tactical/field environments. Frequently, when removing a stethoscope from a bag, multiple other unneeded pieces of equipment will be pulled out by the stethoscope. This is due to the tentacle nature of stethoscopes and the lack of any standard way to pack them.
Further, in a tactical situation, biauricular listening is not necessary. Most providers will be seeking a more basic physical exam finding such as positive or negative lung sounds. That is, there is no need to make specific cardiac diagnoses in the field.