I mean, if you come from a family of alcoholics and you yourself have the opportunity to see the problems caused and the frame of mind to not follow, then why at some point do you follow?
If a person grows up with that environment as "normal", then he may not perceive it as a problem.
Or, he may simply wind up following the patterns he was raised with because they're ingrained into him. Even if he knows better. Imagine how many times people say, "I'm never going to be like my parents!" and they turn out just the same anyway. It's hard to get away from your programming.