Kevlar doesn't stop a knife, and it doesn't even reliable stop a bullet.

Depending on the situation, you'd think a tactical team might be available with beanbag rounds or maybe even a catch pole (essentially a 'lasso on a stick'), but it's not as easy or as safe as you might think.

And not to put too fine a point on it, but how much is a life worth? How many cops do you assign to keep the person away from others, for how long, and what are they supposed to do if the person tries to break through using whatever weapon they have before they pass out from exhaustion?

Ultimately, the answer is that someone's getting shot. And that sucks but it doesn't mean it could have gone otherwise under reasonable circumstances.