It's not easy to just stop gambling, especially if you have become an addict, the only way is to get used to reducing it slowly so that the brain and heart become accustomed to the pressure on our minds to continue gambling, I'm sure people can do that too. like I can also do it because I have the determination to reduce my gambling activities so that I can be more controlled.
There are only two ways to stop an addiction, one way is to do it gradually as you are suggesting, this means that the person will slowly diminish the amount of time and money they spend on gambling over a period of time until they stop completely, however the issue with this is that this requires an enormous amount of self-control, which is precisely what those which are addicted do not have.
The other way to do this is to stop abruptly and never engage on the activity again, and while this strategy also requires self-control, it seems like the best out of the two and it is often the one used by professionals to get people to get their addictions behind.