Personally I don’t think it is our responsibility to try and get someone out of their gambling addiction especially if we don’t really know the person. An advice or two may be good but you do not need to force them nor should you.
Unless they are a family member I think it would be better to intervene, whether they like it or not because most likely your family will be affected as well.
If it's not someone we know or in other words someone from our own family, of course there's no need to spend more time giving advice repeatedly to that person. Because each person also has their own mind to do anything with decisions that come from themselves, so from what you say it seems quite appropriate to apply to everyone who likes to give advice to all gamblers. Because in this world there are also rich people who like to gamble and consider it as a hobby and they are never hungry when they lose from any gambling.
Yes, on the other hand, what you say is true, if the person who is addicted is not one of our closest family members, then there is no need to overdo it in giving suggestions and advice, because it might be quite draining of our energy and time, and in Plus, they are nobody, in the sense that they are nothing more than other people who don't have a close relationship with us. This means that caring for other people is indeed a good thing, but if it disturbs your time then don't continue.
Addiction is a situation that is really difficult to overcome, and usually someone who has entered the addiction phase has a different mindset and perspective towards gambling, and when you continue to force them to follow the things you say and suggest then there is a possibility that they will think that you are too involved in their affairs or their choices, and also on the other hand it is possible that the people you are giving advice to are those who have a good approach to gambling where they can control themselves well, that is possible.