Dessication (drying out) should also be mentioned. Cockroaches are insects of the tropical rainforest and need a moist climate. Of course, they can always find a small amount of water in the dark, subterranean spaces they live in; but leaving open pools of water encourages them to congregate.
So one of the first things you should check in a roach infested home is that the plumbing isn't leaking. A kitchen sink that drips water around it is sure to attract cockroaches, in addition to the fact that there is always food in the kitchen area.