Well for one they're dealing with tight deadlines. They need to be able to turn in on time. For another thing there are many (myself included) who feel they get a better result using higher heat on certain meats. Chicken is an obvious one, as the skin will be very rubbery at lower temps. Brisket and pork butts are others that I like to do at higher temperatures. Less moisture loss, better crust, and very predictable cook times are some of the benefits I've found.