Short answers, pulled from the story.
The term began to appear in the American press during the early 1940s referring to aerial munitions capable of destroying a whole block of buildings. Publicists drew on readers' familiarity with these bombs to create an analogy for huge impact.
This practice was outlawed in 1948 before the term became common parlance. Trade publications subsequently appropriated the term as short-hand for a film's commercial potential throughout 1943 and 1944.
In 1975 the usage of blockbuster for films coalesced around Steven Spielberg's Jaws. It was perceived as a new cultural phenomenon fast-paced exciting entertainment inspiring interest and conversation beyond the theatre.
There are now 43 movies in the MCU with a combined global box office of $31 billion. The franchise inspired other cinematic universes including the DC Extended Universe the MonsterVerse and the Wizarding World.
Film journalist Peter Biskind wrote that all studios wanted was another Jaws and as production costs rose they were less willing to take risks. He argued that studios based blockbusters on the lowest common denominators of the mass market.