Earlier this year, The Wall Street Journal published an in-depth report highlighting instances of thieves watching iPhone owners enter their passcode...
Hardware: The components required are thicker than the display side of a MacBook. Someone commented about the Studio Display (and likewise the iMac), but that’s enabling Face ID just for a fraction of Macs (and could potentially limit future design).
Requires additional physical input anyway: On the iPhone, you swipe up to unlock. The Mac could just accept the spacebar as input, but it’s still a secondary action meaning Face ID is “press here instead of touch there”. It also means that for Apple Pay or anything else requiring confirmation, you’d need someway of confirming (click here instead of touch there).
It’s not solving the problem that the iPone had: Face ID on the iPhone enabled the iPhone to get rid of the Home button which greatly increased the amount of the display area. It wouldn’t do that on the Mac. Really the only thing it’s doing is allowing some other physical action (press the space bar or click a confirmation button) instead of touching the power button.
Face ID on Macs faces multiple problems: