After the success of Jaws and Star Wars in the late 70’s, many Hollywood producers started creating similar "event" films during the 1980’s with wide commercial appeal, and film companies began green-lighting increasingly large-budget films, and relying extensively on massive advertising blitzes leading up to their theatrical release.
The term "Block buster" describe films whose premieres attracted lines around the blocks surrounding Broadway movie houses. As production costs rose, studios were less willing to take risks, and therefore based blockbusters on the "lowest common denominators" of the mass market. Disreputable serials, science-fiction and adventure stories suddenly went from micro-budget B-Movie to more or less epic spectacular productions.