Not just that, but they get to charge $100 dollars more for the $5 of ROM while avoiding the support costs and reputation hit of idiots who force the SD card in the wrong way or blaming the device when the SD card is inevitably sheered in half after being forgotten about during a battery replacement.
Unfortunately every market incentive just aligns against expandable storage in phones.
Unfortunately the US government already took note ages ago. Cross-Industry and general strikes are illegal in the USA.. This kinda thing can't happen here.