We ask a lot of police. They're first on the scene for many of the worst things that can happen to a person and have to handle a lot of people having the worst days of their lives.
And as much as communities try to equip their police as well as possible for worst-case scenarios, it's clear that they just aren't the best suited response to every situation. All too many situations in which a person having mental health crisis required a 911 call have ended in preventable tragedies. We don't rely upon them when a fire breaks out, after all.
Now, when someone calls 911 for a mental health crisis, the biggest police force in the world will have a new and more appropriate resource in their belts to call upon.