There's a massive second-hand market for many general purpose computers. Plenty of people, myself included, buy used hardware almost exclusively.

Beyond that, many people are creating home theater PCs, home labs, home automation systems, arcade cabinets, custom car audio head units, drink robots, and more using commodity hardware. Often times these are reused hardware, which cuts the cost on hardware by a significant margin.

Just because you don't see it happening doesn't mean it's not happening.