B-movies were very popular during the drive-in movie days for two reasons. The first was that you went to drive-ins to make out, which would be difficult if there was a good movie on the screen that occupied the mind of your date. The second reason is that B-grade movies were designed to accompany a "hit" movie. B-movies were produced in large numbers for a small budget, and typically were the thriller/horror genre. The quantity of B-movies produced gave the folks over at the Gizmonic Institute a lot of things to make fun of on the show Mystery Science Theater 3000.