On the other hand: can you name any single occourence where you thought "damn, I wish they would have faded out the song"? I'd daresay no.
I'm not against fade outs per se, but they have to have some kind of meaning, maybe a thematic one - end of the album, the way the lyrics go, anything than "uuh and I guess we just can't be bothered to write an ending for the song, which we have to do anyway to play it live".
Naive question, maybe I'm about to tell a very stupid thing: could it be that fadeouts were so popular to give the chance to the DJ to talk over it and save time? we all know how radios wanted short songs, how Queen had to fight to push for the 6 minutes long Bohemian Rhapsody etc, so maybe a fade out gives a chance to "save some time" since the song is ending anyway.