Betting on skill games can be a lucrative alternative to traditional gambling because it isn't regulated the same way. The legal definition of gambling necessitates the element of chance (the literal gamble in question), and thus, games of skill are largely exempt.
While many casino games are based on luck, there are also games that involve an element of skill. For example, games like poker and blackjack require skill and strategy in addition to luck. However, the house always has an edge in these games, which means that over time, the casino is likely to make a profit.