MGM has Royal Caribbean / Celebrity as their regular partner. Wynn has Holland America. Caesars and Penn have NCL. I'm sure the Semiole tribe/Hard Rock has one as well. Those are pretty much all the big players.
I know someone that "Carnival fun matched" their Diamond Plus at Caesars, which is really not that difficult to obtain, and was offered the same thing I got (detailed above), less the free play and in a balcony room. He opted for a 14 day Hawaii option. Cruise lines are not making money on unoccupied cabins, so they are taking a chance that if you gamble on land, you will gamble at sea.