Because the Police system is a bit overwhelmed. Once they get into the courts the system works the way it was designed. Having sat on a jury, the people that are on juries take their responsibility seriously and make their decision based on what the judge says the law is. If the evidence fits the law then people will convict. If the evidence doesn't fit they must acquit (sorry, couldn't resist).Then why the out of control crime epidemic?
Its getting people to the courts that's the hard part. In the bast year I have been robbed twice, once when the house was broken into and once when I was stupid (internet scam). I reported both to the police and within a week of reporting them the police responded that they were closing the case due to lack of evidence. Unless the value of stolen items in in the 100's of thousands police don't even bother to investigate. The police system is probably a bit more broken than the court system.