I don't think that is because you cannot lose money in free games but it's because you cannot win money in free games even though, gamblers claim to play for fun. One thing that I have come to understand about human is that they like risking the little that they have to get more, but you don't need to rely on it or feel that's the only way out to have funds. So that, you don't get sinked into gambling because the consequence is bad. This is why people are trying to gamble for fun and let go of their losses.