Sadly, you are right. They would rather set up speed traps than do other police work.
Also, in the situation you described, it was a robbery in which nobody was physicially injured, is that correct? It’s possible that such are given low priority by police. I certainly hope a 911 call about a crime in progress would pull the cops from the speed trap job and respond to such a call.
And, as you probably know, most 911 calls about crimes in progress (where third parties make the call and aren't seen by the perps) are typical cases of law enforcement being only minutes away when seconds count.