Flashback rarely gets visitors because of its incredibly stupid location where guests don't even know it exists because of where it is at. The queueing entrance is BEHIND an arcade and low profile midway where nobody really walks through. And plus, the ride isn't so loud and tall that people's attention are centered to it.
But the big kahuna reason of the reason it hardly runs is because of Hurricane Harbor. It is RIGHT NEXT to the park unlike Colossus which is hardly even considered close to it. Flashback and Hurricane Harbor are seperated by a fence, that shows you how close it is. The ride is an Intamin AG ride and it produces sounds that resemble those coming from Kumba and The Riddler's Revenge. Yes, it gets LOUD. So life guards will have a harder time hearing if anybody is drowning and calling for help, not to mention the distraction the loud noises cause.