Simple answer: cheap. That alone would appear to enable many people to throw everything they learned about safe internet shopping out of the window. It genuinely amazes me that people are so comfortable using some of these companies that they will even pay by Bank Transfer.
Take the company names away, would anyone with any common sense use a company that mis-labels packages (content and value), offers money for good reviews and forum posts, has a returns address which is a private residence, has a default answer phone message, basically has a lottery for which plug you will get with your camera etc etc?
A UK company would get a battering on here for far less.