My take on it would be that people see cars for example as a physical item. And that item comes with real expenses. Fuel, parking tickets and whatnot. Your conditioned for this when you get your first car

Mobile phones apart from the device itself are seen as free. Your conditioned to expect to get apps for free, I expect content to be free.

So when you start asking for money; there is no association between the price wanted and a physical object. Only an application which was free.