Why isn't the father given full custody if the mother is abusive towards her child?

Even with a video shown that the ex girlfriend beat up their 11 month-old baby and left him to die among the trash (as a way of getting even after he broke up with her) while the father is heard crying upon finding his child like that.

Honestly, the mother got it off easy with only 1 punch after that guy broke the door. Initially both were charged but then charges against the father were dropped. Then the kid was placed under foster care.

Video:


An update:
https://lightingtheirwayhome.wordpress.com/2015/05/16/daviere-bryant-beaten-by-mother-dalishia-salter-and-left-on-the-back-porch-crying-and-cold-cca0193-updated-05-16-2015/

Updates
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The mother is even heard saying ''I don't care'' when the guy confronts her. The baby is so hurt he can't even cry loudly.
Why isn't the father given full custody if the mother is abusive towards her child?
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