The reason was simple, religious people believed gambling is owned by devils. I don't know where you can find in the bible that states gambling is a sin, I'm not a religious man either lol. I've actually seen people who are somehow involved into a religion that prohibits gambling, but they handle it like it's nothing as long as their fellow people from the religious community doesn't see him or know it then it's all good like it's not of a big deal.
Most of the cases like this, are people who are not serious with their religious belief, it's just that the family are too fond with their religion so one should get along, that's the religious culture here in PH.
But in my POV, there's nothing evil about gambling as long as you don't become irresponsible financially. Also, if one is really SERIOUS about their religious belief, then they should not gamble in the first place, otherwise he is just fooling himself into believing the teachings of his religion.