Because, if you do, the baby will poop on the floor. Then, the baby will crawl over a few feet and poop again. Then, you the librarian will discover the poop and have to clean it up. But you will not discover the other poop in the other corner and it will stay there for two hours until another librarian discovers it. Then, you will be disgusted.
Oh, and just so we’re clear: baby = person old enough to not poop in the corner or anywhere except a toilet or other designated poop depositing facility.