Also, for some people, gambling is illegal in their religion, and most of them want to gamble, so they will rather gamble and keep it secret so that people won’t see them as bad people, so they decide to keep it a secret.
Some people do spend huge amounts of money on gambling, but they are not always comfortable telling people they have spent that amount of money on gambling, so they will just decide to keep it a secret. Some people do tell their friends that they gamble, but they will never show their friends their gambling account transaction history.
It's clear that there is a bigger problem when people hide their gaming activities and costs. Since I'm a big player who plays it smart, being honest is important to me. People are already in danger if they feel the need to hide. Some people might say that spending one's own money is a choice, which is true! However, isn't ignoring family duties a moral offense?
Additionally, regarding religion: while many religious systems forbid gambling, it would be hypocritical to use religion as a cover for an ongoing covert vice. It's important to note, though, that recognizing the moral implications of one's conduct is just as important as being perceived as a "bad" person.
People can always tell bad things whether you live like a saint. And the badder you can be if they know you gamble. It's one reason to justify the secrecy of the activity.
Some of these people are just waiting for your failures to be exposed so they can say I told you so. But I'm not giving them the chance off that and hiding the activity from the government as well since the government is looking into our expenses.