Why is my bed frame bigger than my mattress?

Most bed frames are designed to be slightly larger than your mattress to allowed for putting your mattress into your frame, expansion of your mattress and moving your mattress and bed sheets.

MOST BED FRAMES ARE MEANT TO BE LARGER THAN YOUR MATTRESS AND THIS GAP CAN BE UP TO 5CM ON THE SIDES AND UP TO 10CM ON THE TOP AND BOTTOM especially for American market origin bed frames. 

This is the style of the frames and not a fault with the frame or the mattress.