When we are talking about science, social science, history or other similar disciplines the disparity may arise from the fact most introductory texts present the main ideas which are already well understood and well articulated, whereas the actual researchers spend the vast majority of their time on poorly understood edge cases of those ideas (it is almost tautological to say that the harder and less understood part of your work takes up more time since the well understood ideas are often called such because they no longer require a lot of time and effort).
When we are talking about science, social science, history or other similar disciplines the disparity may arise from the fact most introductory texts present the main ideas which are already well understood and well articulated, whereas the actual researchers spend the vast majority of their time on poorly understood edge cases of those ideas (it is almost tautological to say that the harder and less understood part of your work takes up more time since the well understood ideas are often called such because they no longer require a lot of time and effort).