Because that can introduce anxiety and second guessing in even the most self assured person. Which is good from time to time, but not when you're trying to figure something out.
Unless you've experienced such an open environment, I wouldn't imagine you'd understand the advantages of not working in a state of secrecy. After all, the modern tech work place is an aggressive and hostile, often very competitive environment, right?
Well this open-screen policy puts a stop to that hostility and competitiveness at a group policy level, and as a result: folks are less competitive and more cooperative. This manifests in a much better group dynamic, and higher levels of productivity occur.
Try it! Or, if you find yourself resisting the idea, take some time to reflect what, exactly, this represents that you are afraid of ..
That's a big maybe to base these things on, and most available data seems to indicate that ability and confidence don't really correlate all that well, and even incredibly successful people struggle with mental health issues.
We don't live in some kind of a fair world where competent people are rewarded with happiness and confidence, and incompetent ones are made anxious. A casual perusal of history makes this instantly obvious.
> if you find yourself resisting the idea, take some time to reflect what, exactly, this represents that you are afraid of
Seems like you have already made up your mind and are just seeing what you want to see.
The statements you make here are not falsifiable and seem to be is-ought and wish fulfillment. They don't seem to be based on anything actually real.
And, there really is nothing wrong with this policy of shoulder-surfing - unless you have things you need to hide about the way you work.
Ask yourself: what's so scary about sharing your work this way with your colleagues in a professional environment? There aren't any productive answers to this question .. only emotional ones.