You can find a lot of adrenaline junkies in a casino environment. The thrill of winning money in risky situations is both very stressful and very euphoric - when it turns out your way. You also tend to find many elderly people who have a lot of free time and extra money on their hands so that they can afford the hobby, pass the time, and aren't betting the mortgage money.
Gambling is more popular with some cultures, including some Native American and Asian cultures. In those cases, it is more socially acceptable and traditional, although as more and more casinos open across the US, it's becoming socially acceptable everywhere.
The effects can be disastrous. The high people get from winning is addictive, so they can get to a point where they are always chasing the last win, or staying in the betting until they "win back" their original stake. Most times they never do.
On the positive side, gambling in the US has put hundreds of millions of dollars back into the hands of tribal governments who then, at least sometimes, use them to fund social programs that help out long neglected tribal social needs.