One strong reason for wanting to take over the entire supply chain isn't profit on the front end, it's making sure you can squash anyone who will repair your devices by using the government. This keeps people coming back for a new phone every 2 years as the cost to repair a new one rises up above the replacement cost. (Some people will pay more than a new phone to keep certain things)
Another is that their bet on China and the subsequent doubling down was a huge mistake, in retrospect.