I always like to point out that a problem here is that people don't always recognise it when intellectual effort happens. Most people talk about someone being intelligent because they can get good grades without studying or similar. But not studying doesn't mean there's not an intellectual effort. In fact, most intelligent people are intelligent or stay that way because they are constantly listening, analyzing, learning and thinking in their day to day. Then maybe they don't need to separately study a subject that much. They are used to learn and they already got it. (you get the point)

So, I don't think it's strange, it's usually very different to the "physical training" example, because people don't see it directly.