The PURPOSE of the trigger is to actuate the firing mechanism with the LEAST possible chance of disturbing the proper alignment of the gun in relationship to the target.
It should NOT be unduly difficult to pull, otherwise the alignment will be more likely to be lost, and any shot made to be accordingly inaccurate.
A fair point, but there are a few important other considerations.
First, a lot of recent research with police officers has shown that when they have their pistol pointed at someone, their trigger finger tends to work it's way into the trigger guard without the officer intending to do so or even knowing that it did. There seems to be some subconscious drive to get the finger on the trigger, or at least "check" the trigger.
Second, officers don't train much with their guns. Here in RI, officers shoot their pistols annually. Many of them barely qualify after a day of trying. Given that budgets are shrinking and officers face an increasing number of tasks, we can see why firearms training gets put to the back burner. If they ever need to actually draw the pistol, they are going to be a bit excited. It's easy to tell them to keep their finger off the trigger until you need to shoot, but that does not mean it's going to work out that way. I realize bigger departments probably train more, but many departments in small town USA just don't.
Third, shootings with pistols are usually at close range and rarely is someone trying to make a super accurate hit. In the movies, we often see actors shooting someone in the head because they have a hostage held close. This does not really happen.
All that said, I am not advocating a 13lb trigger like the Glock NYPD trigger. That's nuts. There is a lot to be said for a DA/SA trigger, where the first pull is about 9lb and the next pulls are ~4lb. The Sig DAK system, where the trigger is a consistent ~7lb is a fine system as well. These pulls are a reasonable weight and length, not ~5.5lb and very short like a Glock.
Also, don't forget the potential for AD. I don't have any stats on this, but it just seems that when I hear about an AD it was with a Glock. Maybe because a Glock is so popular. And then, there is the young officer in Tennessee (I think) who came home from work, placed his gun belt on the kitchen table, turned to kiss his wife, and was shot to death by his toddler son who had no trouble pulling the trigger. Bad gun handling to be sure, but familiarity breeds complacency more often than contempt.