Longer growing season. Merican roaches are water bugs. If you eliminate the water source and set some roach motels the problem goes away if you are not overly infested. The problem with living in dry areas is civilization brings water so, things that normally wouldn't live in any real number are artificially increased by the water source, watering plants, water bowls for pets, pools etc.., etc. However if you have the DIRTY GERMAN COCKROACHES
@Maysam DIRTY DIRTY DIRTY GERMAN!! Then it's a hygiene problem. American roaches are leaf shaped and flat. The Nazi roaches high step on your sleeping face, and poop on your lips while in their nazi helmet shaped bodies.