The rear door sits behind the stand / upright part of the press. You forgot this was for a drill press? Storage is divided in half. John designed it to utilize as much space as possible.
I'm sure it could have been built with no rear storage, using the upright of the press as the rear of the cabinet. However from the projects we've seen John do. He tends to over design them.
1 drawer, great, TWO drawers AND Rear Storage, EVEN BETTER!