For those doing it for fun or entertainment they mightn't find it easy to quit as well because when they get addicted they will have similar behavior like those playing for money. They won't want to quit even when they're not making profits. Addiction is very hard behavior to quit.
You have a good point as if it's already turn into addiction so it's no longer just for fun or entertainment but most with a desire to continue playing and control is no longer from that person itself, and it's very possible as you said, when you already engage and you are unable to control yourself then it will be too difficult to quit.
Yes I have seen people that started gambling just for fun and entertainment but as time went by they became addicted that they can't stop gambling even when they're not making money from gambling. They just do it to fulfill a desire in their life because of how sorrowful it is.
Some gamblers gamble because it make them escape reality. The fact is that people are passing through alot in life that if they decide to tell you, you won't blame them for the decision they're making. Bars get filled always it's because people are use drinking to ease their pains.
People use gambling as a solution to their pains, when they win that's the only happiness they get in life and always want to play more so they win and get more happiness then it becomes a habit and they keep playing which ends them getting addicted and hard to quit.