Because they really couldn't get any lower in the quality chain without seriously impacting their customers in an obvious fashion.
I disagree with this entirely. First of all, there is no incentive to buy
low-quality materials. It's obviously nonsensical. What they do try to do is
buy the highest quality materials they can for the cost they're willing to
spend. If they could lower the quality and no one would notice, why don't
they?
Of course not. It's pure economics, and that's why your analogy is wrong.
Talk about picking a bad analogy.
Actually, it's really good, just not a good one to pick because most people have serious prejudices about the food market, just as they do about the medical market. Fast food restaurants provide an excellent product at a very low price. Yes, it's not the best possible product, but nobody could produce that at the same price point.