Because money is the most important to us to live a wonderful life in this world, having a discipline to manage our money is good although we are also gambling and we consider that as fun for us not to risk our finances and might ruin our life in the end.
But if you think twice you would realize that gambling is not really needed in our life. Yeah it can make us fun but there are also consequences that we need to accept. We are going to get addicted if we don't know how to manage our self.
Your thinking is indeed correct. Because of the nature of gambling will only give vague pleasure, so if we do poorly then gambling it is certain we will get a very large losses. Profits in gambling is only temporary, so if you can't give a good game then it will make you a big loss