There could be a hundred and one reasons why a gambler could possibly lie about their gambling losses, some of those reasons could actually be reasonable and some might not.
That's true. Well, as long as you don't owe money to anybody then it's fine to keep it a secret especially if their words can't help you to move on.
for instance, if a gambler gambles with little money that they can actually afford to lose, and maybe they eventually lose that money to the casino, there would be absolutely no point having to lie to others about that lose because it's a minor loss that antone can experience.
There are people who don't like to expose themselves as a gambler and be criticize for being one. So regardless of the amount of losses, they just keep mum to avoid judgement from others. I think it depends on the situation because there are scenario wherein lying is the best option to avoid further problem.