What would the motivation be behind lying or creating a hoax such as this?

Well, people don't like to have to obey rules. The way I see it, someone came up with a theory that threw a God of morals out of the picture, so then they didn't have to have the responsibility of obeying his commands. Of course, there's been more evidence that has made the idea of evolution more ridiculous, but people don't want to 'lose their freedom' by submitting to a God and his rules, so that would be the motivation that I would refer to: Inventing evolution as a way to get around the concept of a Holy God.