Originally Posted by redsof72
Reds wanted to keep him at shortstop to improve his mental understanding of the overall game itself, an area they felt he needed to improve upon to be a good major leaguer, and they felt keeping him at shortstop would keep him engaged in the game mentally at all times, as opposed to standing out in the outfield. That was part of it--straight from an extremely top-level source.
Also, as stated by Nemesis, Hamilton was right on the verge of taking a big step forward as a hitter (which he did) and they wanted to let that happen without clogging up his head worrying about learning a new defensive position.
It's also not a move you make lightly or in a vacuum. Hamilton is a dynamite athlete and I'd be surprised if the opinion inside the organization is anything other than Hamilton could have been a successful SS had he stayed there. It might have taken extra time for him to get his defense sorted out. It might not have been his optimal position. Yet in sports you usually have confidence that an athlete like Hamilton will make the leap (certainly that's what the Reds are thinking with him in CF).
So you probably don't rush into shifting a kid you fundamentally believe in. On top of that, the organizational picture at SS and CF affects the decision. It may have taken extra time to decide that Hamilton is going to be a better fit for the Reds at CF. In other words, they resisted making the shift until they were sure. Drew Stubbs and Zack Cozart's seasons might have played significant roles in this decision.