Control
Think of a sports event. If there were no umpires or referees to control the game, there would be chaos. They may not catch all the fouls, but they catch enough to keep the game under control.
Think of those cities with high crime rates, like Chicago or Baltimore, Detroit, or Los Angeles. If there are not enough police (refs and umps) to monitor and control, crime will continue, and murder rates will continue. So, if you have a chance to curtail or slow down crime and murder in your city, why not take it.
The use of Federal forces in Washington, DC has, to date, curtailed murders and is making DC a safer place, vs being one of the most unsafe cities in America. So the question remains, do I ask for assistance to make my city safer, or do I insist that the use of Federal forces infringes on my State’s rights.
What is more important, fewer crimes and murders or a continuation of the status quo?
Nothing is more important to our Federal and Local government than to keep us safe?