Of course they can't do anything about a crime that hasn't been committed. Do you want police to follow people around to prevent crimes or arrest people they suspect will commit a crime.
As soon as they witness a crime they act. If you expect more than that you are looking for a police state.
Right, it's not a good representation of crime, because the number of reports are always higher than the number of cleared cases, hence the term clearance rate, which by the way is highest for crimes against persons(murder, rape, and manslaughter) despite the earlier claim that "police only protect capital".
Good thing there is a process to validate the arrests.