The 1994 World Cup killed football in America and Canada once and for all, I think.
There actually was a very good build up, loads of adds showing brilliant skill, the media was all over it, I think that despite the fact that football is the polar opposite of the traditional North American sports in pretty much every way, the public was actually hoping to be taken in by it.
Then they saw two traditional powerhouses in the final and thought 'this is really going to be a fantastic game!'.