When you host luck based games it is all about mathematics.
In sports betting however, it is mostly about mathematics, but every once in a while there will be cheaters. (fixed games) That's a serious risk for a casino.
Plus sportsbetting is probably the most played game all around the world, there are 17 countries that are illegal to gamble but allowed to sportsbet so all in all when you combine a greatly played game plus a greatly run organization, it is just too obvious why people can't wait for pd/stake to start their sportsbook. I would probably bet on it on day one and keep betting there forever.