There is an equation that people can use to calculate fogger use. One ounce of product should cover 1000 cubic feet of living space. Ignition sources that can pose a danger include open flames, pilot lights, and sparks from electrical equipment that cycle on such as refrigerators and air conditioners. Foggers are cheap and generally effective. For these reasons, and because humans generally hate home-bound critters, these products will continue to be in demand.
People often use more pesticide product than labeling instructions warrant.
They are desperate to get rid of the bugs and the cans are inexpensive. Plus, they are inconvenient to use. You must leave the room for some time after they are used. So people may be inclined to over apply to ensure the job is done. Roaches are often found in kitchen areas, and kitchens are often not that big.