In practice, there's a camera in the Tesla that looks at the driver to make sure they're paying attention. If they're not, perhaps fiddling with their phone or looking at something in the passenger's seat, then the system gives a warning and then a strike. Get five strikes and you can't use FSD for the next week or two. So drivers are directly incentivized to keep their eyes on the road because if they don't, they can't actually use the system which would suck for a long road trip.