Why do we date losers?

It seems to be a constant problem that I see around me, both in my professional world and my personal world that I see people with partners who treat them terrible.  There is disrespect, selfishness, a lack of effort, anger, and an overall air of being a jerk. I see people we would consider to be “nice” people, who are kind and genuinely seem to care about this other person.  The other person, the designated “jerk,”  is usually mean, controlling, and screams a lot if it is a female and sullen or angry, rude, and dismissive if it is a male.  The person usually is not open to hearing they are the problem in the relationship and think they are fine.  It doesn’t matter if their relationships are littered with dysfunction, they cannot tolerate being the problem.  It is not love to be screamed at or controlled or hit and yet I see so many people who stay in those relationships.  Some time ago an individual was sitting in our lobby waiting for their partner who was in session.  This individual was listening to their phone and it was loud.  This individual did not respond well to my requests to turn the phone volume down and ended up storming out of the office.  My main thought was how someone picked that individual for a relationship and what that relationship must look like.  My assessment is that a person feels that is what they deserve out of a relationship...to be in a relationship with someone with no respect for authority who tantrums when they are told no or don’t get their way.  The work with that individual who is dating the loser is really to help that person improve their self-esteem and work on the negative beliefs that lend to putting up with these behaviors.  Everyone deserves to be treated with respect and yet so many people put up with so much less. Why?   It isn’t because the other person is so amazing, it is about how the person feels internally.  How little domestic violence would there be if people really understood how they should be treated.  And those “losers?”  They, too, don’t understand their value and worth because if they did, they wouldn’t throw tantrums and be abusive and have self-destructive behaviors.  This doesn’t mean there are personality disordered people out there who are abusive(the Gottmans call them the “pitbull” and the “cobras.”), but most people are just broken and wounded and operate out of a very immature self. 
The question to ask self is how does my relationship reflect how I feel about myself?