It's because people mainly perceive marginal costs in the goods they buy, and they don't consider fixed costs. In extreme cases like software, news, etc, they think "this extra copy didn't cost anything to produce, therefore it should be free", even though the initial fixed cost was substantial.

This leads to some things like perceiving less competent workers' time to be worth more than more competent ones' (because they take longer to do a task, therefore they should be paid more), etc.