That becomes a guessing game for international guests. It can take anything from an hour to three to get through customs and immigration. If your flight arrives at the same time as 3 others it can be a long wait. Easy to provide a flight number and arrival time but harder to predict when you’d reach the pick up point.If they require reservations they would be able to use the size they need when they need it.
It’s possible for Mears to work round it but just another hurdle.