The reason for that is that there is only so much room in recieving, and there are only a given amount of people working frieght at night to put it on the floor. Just having 1 truck come in a day (or even hours) late makes a disaster for the freight crew, who all of a sudden have to make 150 pallets vanish in an 8 hour shift, instead of the usual 80.
Poor planning. As I said, Menards and Lowes don't have those problems.