THAT is a very true statement. Proficiency is the direct result of lots and lots of controlled practice. That skill degrades without practice. Practice costs $$$.
When you combine lack of proficiency, with poor training, and handguns with rather large magazines, under the stress of a live fire situation LEOs oftentimes resort to “Spray-n-Pray”. I would bet ALL LEOs involved in this shoot EMPTIED their magazines
I have a friend who instructs LEO’s in shotgun training. He often says the safest place when they are practicing is in front of them. Not true for some as I regularly shoot with some who are very good but as you mentioned these guys do practice.