The tow company profits... In Muskegon county anyways...
They justify it saying that when a CD (central dispatch) call comes in they stop what they're doing and respond. I've been mid-tow, and have dropped the customers car in one of my stash spots, and taken the CD call. The reasoning is this. If a company takes an exorbiant amount of time to respond they simply get kicked off the rotation. The equals big $$ loss. So essentially, you're paying a convience charge. the convience that you're getting moved to the front of the line.
Similar to ambulance calls... Got a heachache, call the ambulance instead of driving your lazy ass to the hospital. You don't have you wait in the waiting room, you get wheeled in to a spot upon arrival.