I can't imagine the pain and then the joy one would have gone through by betting on Moonlight and having La La Land being announced as the winner at first. The odds were terrible though for La La Land.
They hype La la Land so much that's why bettors think it is an easy money, I don't know if there is a monopoly that happens but base on my observation when a certain bet is a heavy favorites, it would not usually win. This does not apply in Oscars alone as the same scenario happened many times in sports and in politics. Maybe we should have to bet against the public all the time and stop analyzing bets.