A:Answer It is because the motherboard is limited in the amount of RAM it will support. Imagine the motherboard a door and the CPU as the room. Just because the room can hold something as large as 64gb, does not mean the door will accommodate something that size.
Another way of looking at it is that there is a finite amount of data and power that a motherboard can handle. If there are certain electrical pathways that aren't robust enough (or simply do not exist), memory beyond that capacity is redundant and a waste.
