You could possibly need to truly need to comprehend every single sentence in the book, which would cause you to read at a slower rate.
Another reason would be if you are challenging yourself to read a certain amount of books within a time table, then you might have to increase your reading rate.
So far i have: The human rights issues in 'Of Mice and Men' is that Lennie, a man with a mental disability, is treated poorly due to his mental disability.