It's definitely for showoff, but also some do it to attract or influence other people into gambling sites; they are giving the wrong idea to the viewers on how easy it is to earn in gambling sites such as that, but in reality it is not. In short, they usually do it to attract more players and deposit in that site, as well as for referrals. In my opinion, keeping a huge amount of money on a gambling site is not a good idea. There are many reasons why, but mainly that your money could be gone.