You'll notice that Poker is the only game that the house doesn't put money in. They provide the space, dealers, security, and chips, but they don't actually play the game.

There are people that can and do make a living at poker.
BlackJack has decent odds if you know how to play, but then, if you play the right spots in Craps and Roulette, they have decent odds too. But it's just too tempting for most people that start winning to bet on high gain high risk bets. Besides Poker, Blackjack is the next best thing.
You can also sometimes spend hours on the penny slots on little money ($20). The odds generally arn't too bad, mainly because most people put everything they win right back into playing. People don't play penny slots because they want to win, they play them because they have nothing better to do with their time.