I've answered this before, but two reasons.....
1. SOMEBODY had to play the guard/wing spots in practice on the 2nd team, since Blair was the only true guard we had on the bench last year after Newell left. If you look at the players that were on the bench, redshirting, or walk-ons, the numbers game simply pushed M'Baye to the wing in order to have a decent 2nd team.
2. I don't doubt that LK wanted M'Baye to improve his perimeter offensive game, and what better way to do that than to stick him out there full time? The confusion comes in that some folks think that means playing him on the wing this year, while I think it means playing him as a post that can step outside in the flow of the offense. That isn't some new thing. Ace, Minor, and Najera all played minutes as the "4", and were able to score when getting the ball outside the three point line. I think LK was just trying to improve M'Baye's skills out there, by giving him as much time on the wing as he could.