Detective shows are all hyperbole. If the case doesnt fall into their lap, the criminal is getting away. Luckily, most crimes are done by egotistical people who cant help but give themselves away, but there are a lot of unsolved murders that very clearly were done rather sloppily and investigated even worse.

At the end kf the day, a job is a job and not every police department in the nation can afford a Sherlock. He probably works in a scientific field anyways