It's a cultural thing. For some folks it's a part of the natural order of things.
If you grew up learning it's proper to discipline beat your kid until their legs are bruised with lash marks then you don't think anything of it when your a sports star is arrested for doing the same thing to his 4-year-old.
If you grew up learning that womanizing is a natural and expected thing for men then when your sports star does the same thing you don't think much of it.
If you grew up learning that husbands or wives slugging their mate as a method of sharing frustration or winning an argument is natural and normal then when your sports star does the same thing you overlook it as normal.
The NFL is populated with individuals from a wide array or cultures. But one culture in particular appears to be dominating the news in this regard, and in each case I see the aformentioned tendencies at work. That culture is not the only one with these issues.