Because an unlocked car is a situation that can be addressed while a locked car is one that can not, likely reducing the overall number occurrences. Also, an unlocked car is a lower barrier for a potential thief as well. They may choose to pass up a locked car while an unlocked is a much easier target.

> Because an unlocked car is a situation that can be addressed while a locked car is one that can not

They could, by the same logic by which they steal (er, "confiscate") goods that are visible in unlocked cars, just tow away locked cars that have visible goods in them that are an "invitation to thieves". Or, for that matter, locked or unlocked cars that, by their value and ease of theft are, themselves, "invitations to thieves".

Or they could get one of those key fob repeaters to unlock any car with a keyless entry system if the owner is nearby.

I doubt it. From the description of the "caretaker law" presented in the article, it only allows for this sort of behavior for an unlocked vehicle. They wouldn't have grounds to tow a locked vehicle because leaving valuables in plain sight in a locked vehicle, while stupid, isn't a crime.