Curiosity and free time. Often I want to find out how big my luck is today by placing small bets on gambling machines with high risks, such as slots. Measuring your luck today isn't bad, as long as you don't waste too much money on it.
Free time is also the main reason, where when I have a lot of free time, it triggers me to do things that are not useful, such as gambling and other sins. So, I think it's an opportunity for me to gamble.