Upvote:-2
Seattle was a progressive city, and the fair was on a progressive topic; the coinciding of the two was the greatest reason for Seattle's selection.
Upvote:6
The idea for the Century 21 exposition originated from within Seattle itself. "A defining moment in the history of Seattle, this fair began life as the brainchild of City Councilman Al Rochester." (source)
To quote some other relevant details from Wikipedia:
The fair was originally conceived in 1955 to mark the 50th anniversary of the 1909 AlaskaβYukonβPacific Exposition... With the Space Race underway and Boeing having "put Seattle on the map" as "an aerospace city", a major theme of the fair was to show that "the United States was not really 'behind' the Soviet Union in the realms of science and space". As a result, the themes of space, science, and the future completely trumped the earlier conception of a "Festival of the [American] West". In June 1960, the International Bureau of Expositions certified Century 21 as a world's fair.