Why do women have kids with guys that leaves them single then turn around and expect the nice guy to help out?

Because i have a friend who really liked this girl and she ended up dissing him for another guy (who is currently in jail for drugs and firearms) who is a knucklehead. They are both 25 and my friend is 27. Three years ago she dumped my friend for this fool and they ended up having two kids together. The problem is he has been in and out of jail since he was 15 and never had a stable Job to speak of. He ended up going back to jail this year for 5 years because he pulled a gun on a crowd at a nightclub and shot at a guy in the leg.. He was always this way even before we knew him but she liked him fo some odd reason.. So its been 5 years later and she is trying to come back into my friend life who is now successful with a good Job. She said she didnt know what she was thinking and now wants to be with him because now she realize what a good catch she missed out on. I told my friend to kick her out to the curve. I just found out she is being EVICTED from her apartment because she has no job and no money to pay for kids to have a roof over her head but yeah, why when the going get tough girls always like the nice guy but only as a safety net when things goes wrong?