Well because in fact, if you are just keeping it to yourself, and lose money, your behavior would change, your loveones would ask you what's happening in your life and you won't tell anything about gambling. You are basically lying to them and that will be an endless loop until you confess to them what you are dealing with. Carrying that burden would only make your life harder. Because you won't be getting the support or understanding that you need from your family. Regardless if what they have for you is a support or neglect, you must still have to tell them. That's too heavy to carry. So talk things to the people who are important to you. Live your life and don't let gambling take it from you.
As long as they can prevent the changing of their behavior, they can keep their gambling activity in secret and no one will knows about that. They can playing gambling without any one knows and disturb them and they will not breaks their limits because that's the important things for them. They can keep their gambling activity secret but they will also needs to learn about self-controls so their gambling activity will not makes them lose much money. But many people can't realizes about that and willing to still playing gambling without control and that makes them becomes addicted to gambling. If they becomes addicted to gambling, that will be difficult for them because their family will knows that from the changing of their behavior and will asks them about what's going on with them.