It’s because the higher you are in the chain of corporate command, the less time you have to dedicate to each task. You end up with shorter answers to every note because you wouldn’t have time to reply to all notes and do the strategic things you need to do, otherwise.

As an individual contributor on a team, you may have to interface at most with 30 people on a weekly basis. As a second line leader you may have 150 people under your purview, and another 50 outsiders you have to talk to. You can’t scale the amount of time you have, so you scale the amount of time you spend on replies.