Well, if they don't chase, the offender will, in the vast majority of cases never be arrested.
If there's no pursuits, why would anyone stop? If i told you you could get away with speeding by just not stopping, would you pull over for the police? Why, then, would someone who'd committed a more serious offence?
Pursuits in the UK are very strictly managed. Only specially trained officers in suitable vehicles can pursue, and even then they'll be strict rules on what they can and can't do. All pursuits will be risk assessed both by officers on the scene and need authority from a senior officer. If either decide the risk is too high, the pursuit will be stopped. If the senior officer does not believe the pursuit is necessary (eg, the driver is known and can be located later) the pursuit will be stopped.