One of the things I've learned from coaches is the Number One thing they want after hustle is consistency, especially from their point guard. Pitino specifically mentioned that consistency was a challenge for IW. And when coaches are talking about consistency, they're not just talking about in games. They're especially interested in the day-to-day consistency and improvement shown in practice. As mentioned before, what you do in practice has a huge influence in your playing time where Pitino is concerned.
Obviously, I wasn't at any practices, but it seems like coach could never feel confident on which Isaiah was going to show up at practice, and therefore games. There were times I thought IW could have been helpful, but wasn't in the game. There were also times when you watched him get torched time and time again on defense and wondered if he would ever play again. And finally, there were times where he was a magician in dealing the ball for easy buckets. That's the point, from game to game, (and I can only assume from Pitino's comments during the year, practice to practice as well) you never knew what was going to happen when he took the floor. Coaches generally can't stand that, and if it never changes, they'll go with the known rather than the unknown.
I have no doubt that IW will find a hoops home (probably not the Big 10) and will end up having a nice college career. NBA? I would think that unless he gets bigger, or much, much better defensively, he'll likely need to become a Curry-like shooter to play in the NBA.