[maccard]

Because it's a smaller upfront cost, and a "pay per usage" cost ongoing. Many people don't want to (for example) dedicate the space to a large dvd collection for something they're only going to watch once, or to buy a media cupboard to hold two extra dvds. People don't want the hassle of reselling/searching the second hand market (where companies like eBay provide value, but friction and risk at the same time as anyone who has ever had an "item not received" case opened against them will tell you).