Station Casinos owns and operates Red Rock Casino Resort Spa, Green Valley Ranch Resort Spa Casino, Palace Station Hotel & Casino, Boulder Station Hotel & Casino, Santa Fe Station Hotel & Casino, Wildfire Rancho and Wild Wild West Gambling Hall & Hotel in Las Vegas, Nevada, Texas Station Gambling Hall & Hotel and Fiesta Rancho Casino Hotel in North Las Vegas, Nevada, and Sunset Station Hotel & Casino, Fiesta Henderson Casino Hotel, Wildfire Boulder, Wildfire Sunset Casino and in Henderson, Nevada. They offer Princess Cruises either free or at discounted rates depending upon your play.
Caesars Entertainment (previously Harrahs) owns and operates casinos all over the US including riverboats and are generally named Harrahs . They offer Carnival Cruises either free or at discounted rates depending upon your play.
Both casino chains used to have giveaways with semi-expensive "junk" that they gave away on a regular basis. The cruise program allows them to reward their customers with a better "prize" in the form of a cruise and I would guess they are well compensated by the various cruise lines for sending casino players..
Go to the casino websites and see benefits tabs.