Because it would give people that took the perks the ability to shoot and run at the same time in RT, giving people trying to run away no chance at all to do so, because theyd be getting shot as they ran, restarting the timer every time. Instead it could be a slightly faster run speed (as that's pretty much what is represents anyway) so that if they are being chased in say an encounter, they could run, stop and then fire before running again, or in a pvp encounter, get away quicker, or be able to catch up to slower people and wait to fire. When your running as fast as you can, you really shouldn't be able to fire aswell, but if your just walking away, there shouldn't be an issue in taking a shot, obviously you couldn't do it as fast as if you were standing there, but it's still possible.