They are leaving the “why” to debate, and I’ll be glad to break the ice.
I can think of two possibilities right away:
(1) If the cops know they are on camera all the time, then they will restrain themselves in such a way, when they are up against hostile and belligerent civilians, that will make themselves more vulnerable to assault and battery by the civilian against the cop. Just as it has been proven that white cops are really trigger shy vis-a-vis black civilians because they don’t want to be Darren Wilsoned.
(2) Geographical bias. The sort of agencies and jurisdictions which implement cop body cameras tend to be ones that implement them because of race-based political pressure, because the citizens think that the evil white po-leeceseseseseses have declared war on black babies’ bodies, and the they think the cameras will catch them in the act. Therefore, of course cops that wear cams are more likely to be assaulted and battered than cops than don’t, simply as a function of the fact that the places where cops are made to wear cameras are dinduistans, and there are more civilian-on-cop A&Bs in black areas than white areas simply because there’s more crime overall in black areas than white areas. The A&Bs would happen anyway even if the cops didn’t wear cameras, once again, because dindu.