The reason could be as simple as chasing the losses. Maybe deep in his mind he is still thinking about the losses that happened to him and he want it all back. There's no way this could be managed by anyone, it's only the gambler himself that could make the change.
He must start forgetting about what happened and all the losses. There's no assurance that he can get it back so it's best to not add more problems.
I think that if the loss is big enough, you won’t be able to forget about it, and subconsciously you’ll want to win it back. But this looks like a trap, because to do that you would have to return to gambling, and if you couldn’t win before, you also won’t be able to when you come back. And that means you’ll lose even more, which starts to look like some kind of dead end, and if you understand this, you can avoid it.