Most of us don't fly every day. And theft, vandalism, and critters are much more likely to occur overnight than during an hour you're eating a $100 burger. If the plane sits for weeks on a crowded ramp, you're much more likely to have damage occur during those weeks than while you're taking a leak. For the CAP plane, if I just flew the damn thing into base, I'm not spending 20 minutes on another full preflight before flying a sortie. That's time I could be searching, so it gets a walk around and mag check. Following your rules, the AFROTC flights I did last month would have spent almost as much time preflighting than flying the cadets (they are very short flights).