I think its because you can easily doubling your money on gambling but the risk is you also can easily lose your money on gambling. I think gambling is makes more addicting when you win much money on gambling and it's make you want gambling more.
which makes gambling so addictive is not only when we win the advantage, but if we lose any money we would gamble again to regain the lost.
and the third thing is the fun in it, there are more people who do not care about the victory and the lose of bitcoin but they go to these casinos again and again because they feel more fun at there and with that they become addicted.