I will apologise in advance as I am posting on this without knowing all the facts, just some food for thought.
My understanding is that the statistic revealed is the number of convictions from drug related raids; however, we don't know the value of the drugs (or other criminal articles/evidence) recovered during those raids. Potentially, couldn't that 9% be made up from some very large findings?
Recently the news contained a story on a highly substantial finding of Class B drugs and money (which is believed to have been derived from criminal acts).
Even if the success rate appears low, removing high quantities of illegal substances from the streets that these criminals share with our loved ones is surely only a good thing for our society, generally?