That's intended as far as the permissions go. It's done that way to keep things tidy, no more sinister reason. Think of the forum like a filling cabinet - the board as a whole is the cabinet, each major group of sections is a drawer, then each section therein (say a particular engine, etc) is a hanging file. You don't want loss of stuff floating around unsorted as you'd never find it, hence the arrangements. There's nothing in the generic "engine" category, it's all filled under the relevant type
Chat has been stuffed for ages.