I read it to find out how his hate was formed, and discover evil lives in ignorance. "Know your enemy" comes to mind. The opposite of diversity, is Hitler. Einstein did not have to read it to know Hitler was an idiot, and thug.
Why? It is .99, and kids have no clue that is ~1 dollar. Math.
The only book they can buy on minimum wage. They don't know where the library is. The NAZIs forgot to burn it.
.99 cents is a big reason.
Ignorance is the other, they don't know it is free on the Internet. Why pay for it, when you already pay for access to it.