I've always wondered that too. I've often suspecte the reason that some agencies use the Glock versuses others is related to a variety of factors including agency size, types of personnel in the agency, and time spent devoted to firearms training.
For instance, it makes since that the Border Patrol would issue Berettas and HKs because I can believe they devote more time to firearms training whereas the FBI has a whole of sworn gun toting agents that might never ue thier piece in the field and as such, can get by with the lowest, cheapest common denominator, such as a Glock.
NRA Life Member
Big Sister: "You should be sponsored by Allen"
Me: "If you can't shoot good, at least look good walking to the firing line."
Big Sister: "Can you not afford a Pelican? Then buy an Allen gun bag."