From memory, the fuel tank vents are internal. The caps probably pretty well seal up.
Fuel leaking from a cap, a vent, or even a severed fuel line is more like a trickle. (Taking 10 mins + to empty the tanks at a guess. And depending on the angle leaving some in the tanks.) having the tanks sliced open by a broken flex plate could have the entire contents onto the hot engine/two magnetos in seconds. Two very different scenarios.