The longer you are in the casino, the higher chances that you lose your money. They make you feel comfortable inside the casino so that you won't think of leaving, that's their strategy.
I agree with that reason, because they want you to stay, until that your money nothing will left, and it convince you more this is why they offer some free drinks. The other reason because they want you to return in their casino, and this can be attract to the gamblers. Because casinos wants only their costumer will return.