> why do they care whether 100% goes to the supplier, or 99% or 0.01? If an item costs me 10USD, I don't care who get's that money, I just care that I don't get to keep it right

But you care if it costs you $10 instead of $9. My point is that Amazon's rules means the price is higher for everyone, in order to cover Amazon's fees. Without them, if you are willing to buy from somewhere less convenient than amazon, you can get a better price.