This may seem like a stupid question, but it's made in all innocence. When you basically know you're going to get rain for the whole day, what's to stop you covering the entire outfield? Ok, it'd be work for about thirty or forty groundsmen, but all you need is a bloody great tarpaulin with, I suppose moveable pillars of diminishing sizes in concentric circles from the middle out to a bit beyond the boundary, to ensure the run off of water.
It'd cost, sure, but it's the Ashes at stake, for heaven's sake!
Is it actually against the rules? What am I missing?