I believe it is just a difference in mentality.
People that gamble think they are unlikely to profit.
People that invest think they can profit.
Look at the stock market, look at small businesses. These people are investing time and money into something, just because they are investing does not mean they will profit. In fact most businesses do not.

Then think about the mentality of people at the casino.
I personally will go to the casino with a starting bank of $250 with an aim of winning $150, but prepared to walk out with nothing. I believe I can profit.
How many people set aside say $100 that they are willing to "spend" at the casino. These people gamble, and have no rules. They have decided before they even get there that they will leave with nothing.....