...Or not. Seriously? That's it? The case design team must have wanted to give lots of breathing room to the motherboard team, just in case. (Actually this is the third version of the internal hardware, the first took up much more of the case.)
Jay Miner was able to integrate the display and sound chip into a single IC, thereby reducing the footprint of the motherboard, but the case size still seems rather hyperbolic.
With a design that is unseen in just about any other electronic device, the motherboard is propped up and sits at an angle of 30 degrees inside the Atari. Now those case screws make sense!