It also comes down to different ways of operating. Police helicopters in the UK generally only fly when called for by patrols on the ground. Each force(apart from a couple) only has a single aircraft which flies around 1000-1300 hours a year.
Compare that to the US, where forces have numerous aircraft and fly routine patrols. For example: New York City Police Department has six choppers and flies an average of 300 hours a month. The Houston Police Department has eight aircraft and flies an average of 450 hours a month. The Los Angeles Police Department flies 18 aircraft, racks up 1,800 flight hours a month.