Actually, I assume the OP is just talking about putting money into gambling sites rather than investing in them. In this case, people generally just do it because they find gambling enjoyable (possibly due to the thrill of the possibility of earning more money even if it is unlikely and they know it).
I would agree, according to some science, there is also an adrenaline pump when you are very much into the odds of where you are betting. It also contains addictive drugs that the body execretes like some nicotine or caffeine. In internet gambling it's not really that thrilling cause sometimes u made no investment to it except your time.
