because they love office supplies.
They did it because they love organizing and running profitable retail businesses. They love hiring and leasing and telling a story that converts prospects into customers. Postits are sort of irrelevant.
You shouldn't become a middle school math teacher because you love math. You should do it because you love teaching.
I hope Staples has a senior buyer who actually does love office supplies. I hope that textbooks get written by people who love, really love, the topic they're writing about. It's easy, though, to fool ourselves into believing that going up the ladder means we get to do more of the thing we started out doing.
It's often the case that the people we surround ourselves with (and the tasks we do) have far more to do with job satisfaction and performance than the subject of our work.