To stay in the charts it must have been selling, just sayin'.
You're right about it being awful, if only because it got played so often.
AFAIK Kris Kristofferson bears some responsibility for it.
It racks up over time but it wouldn't have had the same impact as say Riverdance which was at the top for 4 and a half months. You're talking a couple of thousand each week for 18 weeks. That would definitely account for more than staying in the charts for 90 weeks or whatever in my opinion anyway.
Ah I hope Kris didn't have anything to do with it. If he did then I could see why it sold but he's too good for that kind of a song.