Greed is prohibited in the Bible (1 Timothy 6:10) not gambling. But excessive gambling activity may lead us to sin. Please take note of the word excessive, and may lead.
Yes, gambling is leading everybody to become greedy so it lies down to sin. It creates emotion and that's why it is being generalized by everyone that it's a sin.
Well, it's still an activity that each individual has the power to conquer its negative effect or allow it to control us which is making the others to have a bad ending.
But at the end - everyone quits alcohol - they leave gambling and they leave adultery as well.
There is no goods attached to it.
Not everyone has a success story in quitting and these vices are always said to be attached together but it all depends on the person who is doing these.
Moderation you are right is important but than again there is no control over one's emotion while being into it. so better safe than sorry
That's why not everyone will end up good with all of their overcoming stories. It's being done by many but not all of them are quitting for real and even in the past, the same situations and experiences from different people.