Because it forces them to consider their thoughts, try to figure it out themselves, put their request into one clear sentence that will convey the idea that uses as little time as possible.
Because it forces efficiency in problem-solving.
When you’re there, in the same room, all that efficiency goes out the door because they can talk to you for 10 minutes about the weather, ask you to take a look at the code stop what you are doing, point at your screen, and use you to get them to the answer.
There are probably more reasons, but that’s a big one.
