This is down to the casino generally. Each casino has different deals with providers, so that means they only get a select number of games from that provider, which might exclude certain games. However, it could also be that the jackpot on that game exceeds the maximum payout the casino can award. Thus, they cannot include it on their site. If you really want to play this game, then you should find yourself another casino that does offer it or just settle for a similar game at the venue you are at.