But aren't exclusivity contracts commonplace? Like a contract stating "We'll buy some large amount of product at a discounted price and only purchase from you f

But aren't exclusivity contracts commonplace? Like a contract stating "We'll buy some large amount of product at a discounted price and only purchase from you for the next some number of years." Like Qualcomm could give Apple a lower price now, because decrease in revenue is offset by the promise of future discounted revenue. I don't understand why that's illegal.