You have to consider the thought processes involved at the time!
You are a traffic cop. You pull a guy in a black Range Rover with an illegal plate over for a trivial offence of driving without a seatbelt. A £30 fixed penalty notice, thats it. No big deal. But no, this guy decides he's not having that, and he drives off at the scene.
90% of the time of somebody makes a break for it, its because they have done something far more serious and assume the police already know about it, or will find out about it. Perhaps he's just done a robbery, perhaps he's got some seriously bad stuff in the car? Who knows - all you know is that you pulled him over for a minor offence and he's legged it.
So back in the car, blues on... and he doesnt pull over. He carries on. For 17 minutes.
What are you thinking now? If you are a police officer worth his salt, you are thinking 'Something is wrong here, we need to stop this guy right now'. You finally stop him, are approaching the car. Do you walk up all politely like before? Hell no.
You leg it up, shock the driver by shattering a window, and get him out of the car before he can take off again.
Great, we can pull it apart afterwards from our armchairs with the benefit of hindsight but if anyone here would have reacted any differently they'd make a crap police officer.
What if he'd just performed a robbery and had a load of stuff in the boot? Had you just let him go on his way and caught up with him later you'd never know...