Amateur psychologist here. Fetishism in general is the replacement of or substitution for traditional sexual objectives with an alternative object or action, not traditional in nature.
You either choose, or are genetically or socially programmed, to sexualize a non-traditional source of stimulation.
I would argue that violence is a traditional sexual stimulation source. For a million years, sex often followed the triumph of one tribe over that of another in bloody warfare.
So, your wife is an extension of, and an integral part of ... YOU. When she loses, YOU lose, in a way. A piece of YOU wants permission to be submissive, but your manliness
would be threatened if it was actually YOU losing. So YOU substitute your wife in via your fetish and have her submit for YOU. In that way, YOU can vicariously be a part of the
"sexy" submission without having lost your manhood.
Interestingly, this is also why there are still New York Jets fans. They suffer incomparable vicarious humiliation every week. Only I don't think they are getting off on it.