What's more surprising (I would say, crazy) is that anyone expects more. Nobody works at their top level for more than 2-3 hours a day. Maaaaaybe 3-4 tops. Doesn't mean you can't be productive for many more hours, but you are not gonna be able to work effectively on tasks that are anywhere near the limit of your ability. You just can't and nobody does it....not athletes, not artists, not writers, not philosophers, not mathematicians, ..- not anyone doing hard creative work

Also, for anyone doing that kind of work, things like walking around and socializing is both vitally recuperative and indirectly productive in its own right