[rayiner]

Right. But when someone is stuck and they interrupt someone else, now you have two people who are out of the zone and not working. You have to balance the lost productivity of the interruption against the lost productivity of the person being stuck. (There might be a quite a thumb on the scale of that, because questions often go "upward" to more productive contributors.) Moreover, it's not like the interrupter needs to sit and twiddle her thumbs while waiting for a response. She can switch to doing something else while waiting for a response.

There is a game-theoretic angle to it. The problem is that interrupting someone costs the team, but creates no cost for the interrupter. Individual interrupters have no incentive to try and balance the global cost to the team of their interruption versus their potential idleness.