You're American right?
Maybe you just can't understand it. I don't mean to be condescending saying that, it's just that we're talking about a sport that dominates this country and one we have been rubbish at on the international stage for over half a century. The US main sports of American Football and Baseball aren't really global sports and you don't have 'national' teams as such, so you don't get the same thing.
For the fans to just be absolutely delighted at reaching a final is thoroughly understandable.