I guess it is easier to spend a money that is won in gambling than a money which is paid after a day's hard work.
That depends on how you treat your gambling activity, if you are into business, you would consider your profit as part of your income and you will not spend it right away as you know you are still for a long term and you need to ensure you will last til th end.
Its' different to gamblers who gamble without considering a long term journey because they don't account their winnings and loses.