@odd "de-escalation training, psychology training and social studies" you've hit the nail on the head, these are the elements that I see are missing in current training.
Training can vary by each US state. Police powers are invested in the states not the Federal Government. Another factor is the police are stretched thin on a local level which means they are under a lot of constant stress.
There also seems to be a generational factor which is complex - when I was younger most of the cops had served in World War II or Korea, they had a lot of life experience and did not lose their temper as easily as the youngsters do these days. They were not saints and racism was a huge problem but they didn't fly off the handle quite so quickly.