I think (from knowing some cops) that some people who become cops were the kids in school who were either not the smartest, or who had authority issues and are now very happy to be “tough guys.” Everyone that I know who has been pulled over or had interactions with cops has encountered rude, nasty cops who were unnecessarily harsh in their interactions.
Cops are used to people listening to them and when cops don’t get their way, they can get loud and scary. I imagine when the cop goes home and the wife doesn’t bow down to him, he goes off the rails and starts slapping. Cops also, traditionally, have gone easy on other police officers’ infractions so if the wife of a cop were to call the cops, it would be swept under the rug. Maybe this is changing now, but that’s how it’s been.
In doing the child protective work that I used to do, there was an incident of a police officer’s wife picking up the kids at the day care, and she was drunk. The day care let her drive the kids home (which was very wrong on their part) and then called the cops. The cops didn’t charge the wife, but it did become a report for child protective, plus the day care would have faced serious charges if anybody pursued it with them. Long story short the wife never got her act together and ended up losing the kids, but this is an example of how the cops cover for each other.
Things are changing now, in part thanks to cameras being everywhere and liability on everyone’s part, but traditionally, I think the wives of cops had to just deal with it.