The other sad reality is some women are simply attracted to violent thugs. Last I read, Janay Rice is still with Ray Rice even though he's out of a job. If I remember correctly, she didn't want to press any charges against him.
It's certainly an embarrassment and a PR problem to the league when this stuff becomes public, but it's naive to believe that the league can really do all that much to actually solve the issue of domestic violence. Fines/suspensions may have some limited deterrent effect but they're certainly not going to make these kinds of problems go away and it's really all about send a message.
These penalties are really all about the league making it clear that it doesn't condone this sort of behavior. Since the league is run by a certified moron who issues wildly inconsistent penalties, the light penalties to teams/player in Goodell's good grace are going to be interpreted as a message saying be that "we don't take domestic violence seriously."