I’m can’t speak for anyone else but it was the first time I heard it
I remember referring it and hearing other people call it to the ‘Seinfeld song’. Seems like it was used due to the line ‘unpredictable’ lyrics to connect to the unpredictable nature of the show
Not everyone knows or follow what is the hit song of the day. However I suspect the use in Seinfeld finale elevated it into cultural consciousness where everyone knows the song whether they were interested in music or not.