Easy maybe for those who are doing it just pure for fun and killing some time, but difficult/tough for those who already engage and believing that they can change a lifestyle if luck will back them up and win decently.
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.
The only time a gambler can quit gambling is when he isn't addicted, it doesn't matter if he's playing for the money or for entertainment, provided he isn't addicted, he can stop gambling at anytime. There are some things anybody wanting to quit gambling needs to know.
Since gambling was taking up most of their time, they need a new activity that'll replace gambling. If they find that hobby or activity, then they won't have free time to reconsider going back to gambling. The activity has to be as productive and demanding as gambling was.
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.
Though more on a case to case, as there are gamblers who only play occasionally and doing it completely for fun and entertainment, people who have lots of things to do in life and not going to engage too much time in gambling.