Why not? Apple isn't under any obligation to sell to anyone at a wholesale price, and can apply conditions via a contract when they do so.
Arizona iced tea even prints the price on the cans to prevent people from fucking with it.
Being able to pick and choose your customers (and apply conditions to any sale that favour Apple and disadvantage the customer) is a perfect indication of the level of market power that apple possesses.
Most businesses in competitive industries don’t get to do that.
Any number of products print the MSRP on the packaging. You'll notice it if you peel off the label showing the price you bought the thing for.