Probably because currently they cause more collateral damage than is useful. Your own equipment will be damaged too leaving a bunch of unguided soldiers with just their guns and rations that are still an obstacle an enemy can't walk through, and it will piss off anybody within 1000 miles when you start disrupting their telecommunications with random noise if not cause actual damage. If they are powerful enough you could potentially cause some mistaken nuclear blast warnings too, although perhaps without a gamma ray component it would still be rightfully ignored.