Oh im sure that that reason would be something that would only show up in actual field use (along with the obligatory "Nobody could have predicted" statement) Im split between the  projected beam being too narrow to actually do anything useful, because people could just walk down the sides, either that or  there's a ten minute equipment setup time once you've parked the vehicle its mounted on, by which time your riot has moved somewhere else, (Or inconveniently set the vehicle on fire or something similar)

Any idiot can face a crisis - it's day to day living that wears you out.