I poked around on Google, can't find where I first saw the term.

Many people prefer fixed prices to pay-by-use. Taxis are paid-by-use, but in some cities you can pay a fixed fee to be taken to the airport. Even if people are told and shown that the fixed fee costs more, many will pick it over a regular fare structure because it is fixed.

For the same reason many people pay for phone data they don't need and so on. The value comes from not needing to consider the price once it has been paid.

Some micropayment schemes always had the sense that one was potentially running up a huge bill; Tipjoy had this problem.