Some people will tell you that what you use money for its achievement will tend to last more than the one that just comes on a platter of gold, we should know this for that reason, free things are sometime unpredictable and their value may not be as up to to the quality of what we get when we are actually using our own earned personal money for gambling, i don't know what's behind this, but that is how it has been for some time now.
The concept of money is very much blurred in gambling. The casino tries in every way to instill in the player the idea that his money is just a number on the screen, and that it does not matter so much if it decreases. I think the point is also that any gambler when replenishing a deposit, then internally unconsciously says goodbye to his money, not really hoping that he will be able to increase it and withdraw it back.