Why are Police Helicopters not armed with machine guns and missile launchers like the ones in the military?

Collateral damage. There is no need for such heavy air support, when the confrontation is on friendly territory, Police only use helicopters for searching for suspects and pursuing stolen cars.

Most of the action unfolds on the ground, sometimes in heavily populated urban regions. Missile launchers and machine guns/miniguns could cause major damage to these areas and the people living in them.

except if your in america where gun violence is extremely common.

Police Helicopter's are mostly nowadays used in keeping or tracing criminals faster bairways.