I agree, it is. Gambling is exciting only for real money. Otherwise, you can just play something like three-in-a-row or similar on your smartphone. The whole point is precisely the risk of losing money, and at the same time the chance to win. The demo can also be used if there is some new gambling game to see how it works. But gambling is similar in many ways, and new ones don't appear often.
Demo are mainly for new slots, like when a casino launches their own games, that is when i think using demo is better, but for testing a casino or trying to entertain oneself, if it doesn't carry a particular deposits, then there is no touch of excitement.
The reason for my believe, casinos should have a very low minimum deposits, this will enable gamblers willing to try the casino and evaluate the gaming process, deposit and withdrawal services and customers support as well.