Gambling is certainly an addiction that has strained or destroyed many families. I believe that in some cases, it may simply begin out of desperation for money. A person may need extra cash for something, take the chance at gambling, win, and then continue to try and have this temporary luck repeated. I think for some people, they become addicted to the sense of hope and knowing they have a chance to win money. Even if it's a small chance to win, people like to hold onto that hope.
The impulse to gamble is rooted partly in the dream of getting something for (almost) nothing -- for amassing huge winnings at the cost of a relatively small investment. Humans also tend to like to compete, especially if they think they can be winners. Finally, another reason behind the impulse to gamble is that occasionally some people really do "win big" by gambling, thus making it seem possible that "winning big" is not entirely an illusion.
I think that in the back of everyone's mind is the idea that you deserve something more than what you have. This may underlie the urge to gamble for some; the belief that some supernatural force will act to give you the lavish reward that life has so far not yielded. Most gamblers, while they may be well versed in statistical odds, seem to be operating on an underlying belief that they are somehow exempt from those odds, and if they stick to it long enough, the universe will give them a special gift in the form of a big win.
I don't think gambling is caused by family or peers. I think that it is the rush that makes it popular. We don't have many activities in our modern world in which we risk things. We don't go to war much, we don't have to hunt dangerous animals. We live safe lives. Gambling makes for excitement and something of the feeling of risking something that is important to us.
Gabling can be an addictive activity. People become hooked on the rush of feelings associated with gambling. They want to experience the tension as they wait to see if they won and the rush when they do. Some people probably start gambling because of family or peer pressure. They might start gambling because they need money or other resources. Many people continue gambling because they enjoy the experience. Some continue because they cannot stop.
Everybody likes the thrill of the win, and that is what gambling is all about. Most people also like the idea of spending a little money and getting a much larger return -- again, that is the premise of gambling. All of these things are fun which would be the cause of gambling. The cause of gambling problems stem from trying to re-coup losses, thinking that the "next game" will be the big payout, or just trying to maintain the thrill.