It must be because of the effect of dopamine and the hooking-up effect casino games have onto some gamblers. You gotta remember not all gamblers are the same and there is an important percentage of gamblers out there who are more prone to notice the effects of Dopamine and Adrenaline on their brain.
Remember, dopamine and adrenaline are bio-chemicals substances which are completely antagonistic to feeling tiredness, so they can continue to gamble hours and hours without feeling the need of rest.
The result may be instant on those games, but that does not mean one cannot get hooked up, otherwise there would not be people who are addicted to slots, and there are. A lot.