They are trying to use a technical solution to address a social problem. Train the people to be professional and respectful of their co-workers' time and the problem will take care of itself. Besides, if my incoming emails become too troublesome, I adjust my notifications, and deal with the emails when I need to, not when they arrive. I don't want the company controlling that valve for me. It's a clumsy way to try to address the problem.
Insufficient escape velocity. I keep getting drawn back in, so valuable time and attention can be extracted from me.
Ever notice that even the busiest people are never too busy to tell you just how busy they are?