What about people who go to offline casinos then? They seems to care little about privacy, as security cameras are all around. Or people who place bets using mobile while being on the sports event. They dont hide mobile screens, and with enough luck, anyone could observe what they do. Providers knows every time someone enters a gambling page.
When people try to keep their gambling habit as a secret, I think they do it because they are afraid of shy to give honest answer how much they have won or lost if they are asked. Otherwise I see no reason why to keep it in a secret. If someone asks me if I gamble, I would tell yes. If I find out or know that someone gambles, my attitude wont change a bit towards him. It is his business and adult can do everything he wants.
I think one of the reasons why someone keeps their gambling a secret is because of the environment in which they live. In some places gambling has many negative sides so that people tend to judge someone who gambles. We also know that not all gambling places are legal, there are still many countries that consider gambling to be illegal. So for that reason someone will keep their gambling habits a secret and perhaps only open it to those who like to gamble too.
Actually, this depends on the person and in my opinion whether it is a secret or not is not a problem as long as they can still gamble within very reasonable rules and limits. Even if they keep it a secret, I'm sure there is a fundamental reason why they do that, apart from what I said above, it could also be due to family factors that don't allow family members to get to know gambling. However, whether it is a secret or not, what is clear is that once again I just advise you to always gamble according to the rules and only use money you are ready to lose.