Usually gamblers are born because of environmental influences, because of the influence of socializing and also the influence of prestige... gambling is always present because of trying, then because it is too interesting, it develops into a habit and the longer someone is used to gambling, the longer they will feel that gambling is a part of their life...
You gambled since college, while I'm sure some people here have gambled since they were little, maybe 10 years old... small bets to win something are the seeds of gambling... it is not considered a threat, but it becomes something that reminds our psychology later on to repeat it with bigger bets.