Because one car becomes one car and a boat, and then it becomes one car, a boat, and a project car that is always being worked on. Then the brother-in-law moves it for a while, and it becomes two cars, a boat, a project car, and an assortment of quad-bikes.
Does it always go this way? No. Does it go this way often enough that people worry about it? Yes.
Does it always go this way? No. Does it go this way often enough that people worry about it? Yes.