How do you know that gamblers withdraw most of the money from the casino? As per the surveys and my personal research, I think most of the gamblers will keep the money in their gambling account (casino) as they have to gamble daily and they don't bother moving them out of the casino. Another group of people believe that if they move the money in and out of casino on daily basis or frequently, it will not only add burden on them but at the same time it may add unnecessary withdrawals fee.
While depositing in the casino may not be that costly but withdrawals can be burden if the casino charges high transactions fee. Still I think one should not keep big amounts in the casino.
Can you please drop a link to the research survey of yours so we can have a look into it too to confirm. The bot of you might not be wrong with your interpretations on the matter because every gambler has a different way of thinking with their funds. Take me for example, I make sure I withdraw a good portion of my funds after making a win from my bet, that's because I love it when I purchase something with the profit I make with my bet as it gives me a good feeling. We can't all be alike, you might worry about withdrawal fees another gambler wouldn't care