As others have pointed out, this grace period did not exist before 2017, and prior administrations have managed to do just fine without building teleportation machines or conducting Trump style raids. If someone is in the process of self deporting and can show they are making good faith efforts to leave, there is no reason to arrest them. But there has to be a line somewhere. Another possibility could be interpreting the end of employment/expiration of the visa as the day your last paycheck is delivered. Two months is crazy though.