It's not like he's a human being - more like a tin of soup we've bought and paid for, and we can make it sit on the shelf till we're ready.
Goalkeepers are in a unique position in a team - if Hart is number 2 it means he plays virtually no games. Keepers never get subbed and rarely get injured. A player like Zab may not be first choice for any position but he could still end up with 30+ games. We complain about players who are only here for the money, yet complain when we have players who think playing games is more important than sitting down and collecting a big cheque each week.
Winners don't want to sit on benches, they want to play and get better. I suspect Hart will be number one, but if he isn't then I'd loan him out as it can only do us good for him to be playing regularly and improving.