Or you can think of it in the opposite manner, they could just sell all of the $500 spec'd chips as $500 chips and miss out on an entire market of people that could use a lower spec'd chip at $200.
But that's besides the point. If I'm buying a $500 chip, I want that chip. The one that passed, qualified and is guaranteed at that speed by the manufacturer. I don't want a $200 chip that you hacked to happen to be able to run at that speed.
If you want to buy that $200 chip and hack it to run at $500 speeds go for it, there's nothing wrong with that.
But that's besides the point. If I'm buying a $500 chip, I want that chip. The one that passed, qualified and is guaranteed at that speed by the manufacturer. I don't want a $200 chip that you hacked to happen to be able to run at that speed.
If you want to buy that $200 chip and hack it to run at $500 speeds go for it, there's nothing wrong with that.