Even when you are a cop and need help yourself, the squads never seem to arrive fast enough. Police seldom catch criminals in the act. You depend on citizens to call and report illegal activity. I've had to run 90 miles to a call in a rural area. Even at excessive speeds you can't get their fast enough.
Every officer knows the feeling of a call for a baby that stopped breathing.
If you are blocks away the travel time is far to long. You think of your own kids. That robber or burglary in progress is heart stopping as you try to fly to the scene. It is rare you are on top of a call. Any police officer that thinks they or the department can provide adequate protection is fooling themselves.