But they are. I agree that for something like this, someone trained to deal with someone going through a crisis would be of better use than a cop.
But a cop with the right mentality and training can also do the job. They do do the job. There have been examples of cops doing the job in this thread. There are lots of examples on the internet of cops dealing with disturbed people with knives and either talking them down, or disarming them with non-lethal means. Those rarely make the news because things went right. But these examples are evidence that this shooting was completely unnecessary and bad training being a big factor. You don’t need to be a tactician to know to put distance between you and an armed suspect. And when they fuck up like that, there should be consequences.
You’re right that cops rely on their guns way too much as being the only tool to use. But it isn’t some fatalist event where cops aren’t given a choice to use it or not. Hell, they have more tools at their disposal than ever before.