I don’t think the BOM is the issue. It’s a huge cost to have different variations for different regions, and a huge cost to go through certification for various regions. It’s obviously worth it for iPhone and watch, apparently worth it for iPad although most people I know buy the wifi only models. For MacBooks, even though they now share a lot of design with iPhones, I can’t see it being worth it for the few percent of customers that will pay extra for it on a MacBook.