The bus has somewhat more flexibility in scheduling. One other factor to consider is that other for the NE corridor (i.e., Boston to Washington), Amtrak doesn't own any rail and has to travel on freight rail tracks (which is why the ride is slow and can be quite rough). Amtrak trains also have lower priority than freight trains and can be (and often are) shunted aside for freight trains which is one reason why long haul trains are often hours late. If the Maple Leaf/Empire Service train doesn't make its allocated slot at Buffalo, it may be hours before it can get going as there could be a whole line of freight trains scheduled to travel.