As long as there is no law that mandates that a phone must be unlockable to be sold in US (which probably FCC has authority to insist for) - if there is technic

As long as there is no law that mandates that a phone must be unlockable to be sold in US (which probably FCC has authority to insist for) - if there is technical capability for a device to be unlocked - it is manufacturers' fault and they must comply. Apple chose themselves to have total control over the device, signing and ecosystem - now it backfires.