Cops and docs always work. We can all be arrested, we’re all subjected to the same laws, no matter who you are, and we can all die, We’re all mortal. They’re the great levellers in life, the commonalities of life. Law and medicine.
Also, it’s the easiest form of storytelling. You’re starting with an investigation. You’ve got a plot. Start with a dead body, a missing person. Away you go. Investigate. You’ve got a beginning, a middle and an end, you still have all the same emotions and rules and questions of class that you might have in any other drama or soap, but at the heart of it you’ve got a great built-in structure. I’d also put hospital shows in the same category. Someone thinks they’re going to die. They might, they might not. Our heroes do their best to solve the puzzle. That’s your story scaffolding in place.