I think some of this is a product of efficiency. For example, when eBay started, they were more democratic. But, over time you get a lot of garbage. It’s hard as a user to search through it all. By pushing promotions, they can deliver more reliably to the customer, and it’s easier to build a business from repeat, regular users than it is from random people doing online yard sale-ing every so often. Big suppliers ensure standardized products that are repeatable and sellable.
