You're asking why there's a difference between civil and criminal law. The answer is that some things are disputes between people, and other things are codified

You're asking why there's a difference between civil and criminal law. The answer is that some things are disputes between people, and other things are codified as crimes. Kidnapping someone is a codified crime; having a dispute over a contract (including a lease or other document allowing occupancy) isn't. It could be made into a crime via legislation, but I think my other comment puts forward a decent argument for why doing so would be pretty bad for our civil liberties. (The underlying "why" here is that calling the police for a theft or a kidnapping results in a criminal accusation, while just having a dispute over rightful ownership or occupancy is not itself criminal.)