That's a gross misrepresentation of Flash. A fad is something that is popular because of it's novelty and when it's novelty wears off it loses popularity. Flash is not and was not a fad.
Flash was a technology that allowed you to manipulate vectors and provide animation and other cool things. For a very long time it was the easiest and most efficient way to handle animation for web developers.
Flash lost it's popularity, not because it's novelty wore off, but because new technologies provided better ways to do the same things.
Calling flash a fad is like calling standard def TV a fad. SD TV isn't losing popularity because it's novelty is fading, but because new and better technology is replacing it. That's a big difference.
Flash did and still does so much more than ads. It revolutionized web design. Not always for the better but it involved way more than just ads.
And just for the record, I'm glad it's dying.