Well to be fair, no one is going to be listening to Black Eyed Peas in a few decades while other good singers will have evergreen hits forever.
Those songs we remember from a certain decade are usually the best songs from that time, and therefore we remember such times very fondly.
For example if you go on youtube, a lot of big chart buster songs from the past are ignored however really well liked songs (but got popular over time) have a lot of views.