The thing is, it's not just posters on this board who say "Sanchez has Ace potential", despite the high BB rate, and "high" is being kind.
He's had trouble with walking hitters throughout his MiLB career and was still considered a top prospect by virtually all prospect evaluators.
It seems to me that the Blue Jays decided late last year that Sanchez wasn't improving by being in the minors and decided they'd see if the MLB coaching staff could.
We'll see what happens...