We value predictability. We seek to minimize risk of all forms. And while it's true that we can and do learn in our zone of comfort, it is also true that we don't learn as fast as when we are beyond it. Managers also like to make performance commitments for their organizations that are fairly easily achieved. They add a cushion of error, a margin of safety to their budgets and forecasts.
Good managers look for opportunities to stretch their better workers.
But the risk of personal or organizational failure is seldom very large. Interestingly, everyone's comfort zone is different. The very idea of public speaking or singing can produce moist palms and racing hearts for many. So one of the powerful aspects of teams is that they can project a collective comfort zone footprint that is much larger than any single individual's zone. Both individuals and teams grow and learn faster when they are operating outside their comfort zone.