Maybe one of the main reasons that people get away with animal abuse is because it can take so long to actually go to trial. Take for example Greg Collier's case. He allegedly beat a horse to death while "training" it in 2006. His trial was in March 2008 and ended with a hung jury that the judge declared a mistrial. The case was NOT dismissed which means there could be a retrial in the future.
Update:
Right after I wrote about this case I looked up the court records and found out he is going back for another trial. Here is the official court records page that shows another trial will be held in a few months.