Aaron Sylvester said:
You're acting as though the main component of abuse is physical, when the main factor is
mental. In an abuse situation where the abuse is purely physical, your assumption that the victim can just up and walk away from the relationship with no consequences whatsoever is simply unrealistic.
Abuse is, at its core, mental/emotional. Victims are isolated from friends and family, constantly told there is something wrong with them, that their way of thinking is incorrect (They question their own perception of the relationship), made to believe that they have it good or that they will be worse off if they leave, that they will be harmed, that the abuser will harm himself/herself, that they'll never see their kids again, that the abuser will come after them legally or otherwise, etc., etc.
Other people won't interfere because they don't want to "get involved in other people's business", or they don't believe that the abuse is real, or the abuse only happens behind closed doors and they never even suspect it. Abuse victims, male or female, often deal with the abuse alone, and what support they do get often can't do anything to stop an abuser unless they can somehow catch the abuser in the act or prove they were physically harm (which doesn't usually happen because most long-term abuse isn't physically, and the physical abuse that does take place often doesn't leave marks).
In cases where the abuse occurs is physical and between two mentally competent, healthy people (the case you are mainly presenting), most people do "man up" and leave, because there is little stopping them at that point. But abuse doesn't just strike randomly and suddenly, it occurs slowly over months or years, often putting the victim in a place where they can't easily escape.