At the risk of incurring much wrath, I have known a teacher (a friend) who did not work very hard 9 months out of the year, and then didn't work at all the other three months. I also have a friend, a teacher, who spends significant time not merely grading papers, but improving her curricula, knowledge, and teaching skills. She does so 9 months out of the year. I am not trying to belittle the work that teachers do, but there is a significant amount of time that many teachers are not working. I would assume that is a significant reason for the dot's location on the graph.
The problem is the $$$ plot point. Grade school teachers (in the US) are not well paid. Which is why it attracts the lazy people instead of the ones who would actually put out the effort needed to properly educate our youth. (Not meant to be an indictment of all teachers, just the "bad ones".)
