This is one of those situations where you have to do something.
You have a guy refusing to drop the gun. This means he is refusing lawful commands from the police so he is now a threat to the police and the public.
The Force Continuum
Pepper Spray, Baton, Taser
Empty Hand Control
So they started at the bottom.... Presence and Verbal.
They cannot go hands on or get close enough for Pepper Spray, Baton, Taser.
You can use less lethal like bean bags but this is not done against people with firearms.
Last one on the list... Lethal Force!!
Seems dumb to shoot a guy that wants to shoot himself, huh?
But what if he runs and starts shooting other people in the area? You had a chance to stop him and now you cannot make an easy shot with innocent people in the background.