The problem with price controls is that you're fixing one variable in an arbitrarily complicated transaction, and the people fixing the price are fallible.
So then one of two things happens. If you can transact around the price control, that happens. So Apple signs a contract with Foxconn to pay them a billion dollars and give them a pile of industrial waste in exchange for a pile of new parts. The industrial waste has negative value and Apple wants to get rid of it, but they claim it was worth another billion dollars, so now their "cost" for parts is three times as high because they're de facto including the cost of paying Foxconn to dispose of some industrial waste and then claiming the benefit as a cost.
If you try to prohibit that, first of all it hardly ever works because transfer pricing is a pickle, but to the extent that it does, you now have perverse incentives and inefficiencies. Apple used to get away with charging $100 even though their cost is $10, but now that means they can only charge $12 and make $2 since that's 20% of their cost. Unless they can raise their cost by overpaying vendors for equipment or hiring a bunch of people to dig holes and fill them back in. If they pay $10 for that then their cost is $20 and they can charge $24 and make $4. Making $4 is better than $2. But the customer will pay up to $100 if they have to, and if Apple raises their cost to $80+ then they can still charge $100 and make almost $20. "Cost plus" is a massive incentive to be inefficient.
So now you want to pick an amount instead of a percentage. But now if you guess to low you get shortages, and even if the price you set is alright today, it might not be tomorrow.
So then one of two things happens. If you can transact around the price control, that happens. So Apple signs a contract with Foxconn to pay them a billion dollars and give them a pile of industrial waste in exchange for a pile of new parts. The industrial waste has negative value and Apple wants to get rid of it, but they claim it was worth another billion dollars, so now their "cost" for parts is three times as high because they're de facto including the cost of paying Foxconn to dispose of some industrial waste and then claiming the benefit as a cost.
If you try to prohibit that, first of all it hardly ever works because transfer pricing is a pickle, but to the extent that it does, you now have perverse incentives and inefficiencies. Apple used to get away with charging $100 even though their cost is $10, but now that means they can only charge $12 and make $2 since that's 20% of their cost. Unless they can raise their cost by overpaying vendors for equipment or hiring a bunch of people to dig holes and fill them back in. If they pay $10 for that then their cost is $20 and they can charge $24 and make $4. Making $4 is better than $2. But the customer will pay up to $100 if they have to, and if Apple raises their cost to $80+ then they can still charge $100 and make almost $20. "Cost plus" is a massive incentive to be inefficient.
So now you want to pick an amount instead of a percentage. But now if you guess to low you get shortages, and even if the price you set is alright today, it might not be tomorrow.