They get a product which is worse, but in very non-obvious ways, and has some sort of negative environmental impact that is hard to identify until years later.
Of course it is also up to you. You can always choose to buy from dodgy sellers to save a few bucks.
Brands exist for a reason, to guarantee a certain quality.
Also poverty (lack of options). Think of how the 70% of the population who barely gets by would read your comment on being cheap.
Don't know about the US, but I think most people there shop at Walmart or Costco. Seems to work fine.