If a casino companies has a reputation and a user base, third party some of the time make partnership with them to add sportsbook for their customers with a return on percentage base on the number of people that turn up, more users means the service is going to have more commission and the casino will also have increase in revenue and more people to play and more exposure to people that doesn't like the casino. Some people literally use Sportbooks only but with the partnership, it exposes other users that love sportbooks to try out casino games and that's a win win for the casino.
On the aspect of revenue, I think globally there is an increase in the number of people that do sportbooks than people that play casino. Literally a person who is a sportbooks will easily blend to love casino games but a person that love casino games might not like sportbooks and this why I think casinos have beginning to realize the potential money they are supposed to be making. The two combination is a big business.