One of the best things about reaching the Bill Gates level of wealth is probably being able to say, "man, I really liked this book, I think every college graduate should read it," and then realizing you can literally buy it for all of them.
Nothing stopping any of us from doing something similar at a smaller scale. (though the ability to reach people who we don't know, at a large scale, is definitely much much harder)
How would this, as a "marketing move", make any sense for him - or even be worth his time to do in the first place?