It's just impractical to keep a separate fast track line open in GOT. Most of the time, there is only a trickle of priority passengers (i never have someone in front of me when i use it) and security staff would just be bored.
Much better to spread the resources you have and then let priority passengers cut in line (there is a sign explaining this practice too). I never have any problems in GOT regarding fast track (>50 flights per year out of GOT)