That's nothing new but human nature.
If a gambler wins big, he does not win just the money but your friend in him (the person you knew) loses against that gambler. And he thinks that the society may come and ask him for money because he now has that class to lend people, but he doesn't want to. So he decides to stay away from his friends thinking that it'd be better to sideline them and enjoy his life on his own, with some new friends of his category.
I think the decision of some gamblers to avoid friends after huge wins is determined by the gambler's kind of friends and how good they were to the gambler during the bad days that he wasn't winning. For instance, if he has a group of friends that are not good in giving to him when he didn't win big and was probably starving just to save money for gambling, he'll definitely not want to give such friends money when he finally wins big and would do everything to avoid them. Also some people who aren't friends to him would automatically claim to be friends because he's won big and when he avoids such people, they claim he had abandoned his friends because he win big