Because its easier to kill people when they're closer together, no running around the house, just shooty shooty at the bottom of the bed and murder death kill two birds one stone. Saves bullets (or your prefered method) and time.
My parent's bed has a drawers underneath but if you go to the foot of the bed there are cupboard doors that lead to an open space between where the drawers from each side are. When my mom babysat when I was growing up I always played hide-and-seek with the kids she was watching (not even going to lie and say I wasn't totally still doing this in high school) and because my mom keeps a long blanket that covers the doors up you can imagine the number of extremely confused children when they couldn't find me and my mom would send them to the bedroom where I would fling the doors open and exclaim "HELLO" loudly.
No ones gonna try to push a bookshelf