Right. Santa Clara County, California, has a mandatory 10-day quarantine for anyone arriving from more than 150 miles from its borders. This notice is posted in the airport but aside from that there is no framework for enforcement. It is not even all that easy to figure out what territory is outside this zone and the county does not provide a map.
Yea, we really should stop saying things like the government “requires” or “orders” something, if at the end of the day it’s not being enforced. No US state [EDIT except maybe Hawaii?] seems to have any kind of actually enforced public health rules around COVID besides business closures, where enforcement is spotty at best.