I think it's mainly just mom and pop stores around the country, that just have this stuff on store shelves for 5-10 years and it gets pushed to the back of the shelf and forgotten about.
They go out of business and then all the stock is sold off, they then get bought by warehouse managers like above and then get sold on ebay etc.
I tend to buy the same stuff over and over if it's a mundane item like a smart phone or a microwave etc so I make use of this a lot.