Why Do People Not Believe?

I have been here before, but many years ago.  I was so lost, I didn't know where to turn.  I found friends here that I wonder what happened to them.  I got to the point where I was in a good place, way better than ever before.
In recent months, my son has been telling me he doesn't want to go to his dad's.  After a 4 year custody battle in which he only wanted the older one, he treated the younger one with disdain.  Lately he has been violent.  Years ago, officials didn't believe me or the kids, no matter what happened.  Twirling penis in front of them?  Locker room behavior.  Not giving them asthma meds?  You can't prove it.  Scarring son's face after putting him in a chokehold?  Roughhousing.  Now, kids are almost teenagers, and younger son has been choked, had his face stepped on, slapped, and ridiculed. 
I got a protective order for 3 weeks.  Then a judge let the kids go with him provided he is "supervised" and my younger son was screaming and begging not to go.  In the courthouse.  Cops did nothing.  He hasn't been charged with choking him.  Even though both boys gave forensic interviews.  What the hell does it take??????