Why does flooding cause all plants to die out or wilt?

Plants need gas exchange in order to survive. A flood is an extreme case of 'over-watering' and cuts off gas exchange between the plant roots and air. This is even more the case when the plant is submerged underwater -- stomata on the plants surface cells are unable to do gas exchange and therefore are unable to perform chemical process due to lack of carbon source and build up of waste. I'm not sure about this, but I think the cells might also lyse (burst open) due to the hypotonic (lots of water outside cell will cause it to move in) environment. However, there is a waxy covering (cuticle) on epidermal (outer) plant cells that would probably protect them from it.