Same question posed in the Aug. issue of Rider mag. Pg. 84. Bottom line is a couple of things: 1) road crown and 2) longer sight lines on left hand turns equates to higher speeds in the lefties therefore more wear. Goes on to say that in previous days m.c. tires were able to be turned around to even out the wear.
I read about both of those scenarios in the article where the link is provided above, by Vanamal. However, if either of those hold true, then it would be happening to everybody on all their front tires and not just a few people once or twice in their life.
This is the first time that this has happened for me. Also, Ernie mentions San Jose JC (many of the Nor Cal members of this site know him even though he's not a member of this site) had this same thing happen on his previous front tire (he's riding a regular Road Glide) but not on this one. So far, no theory makes any sense. I'm at the point now where I can't wait to get the next front tire on it, just to see if it happens again.