Not many casinos have a demo mode at the moment they probably rely more on streamers to attract new users and the demo mode is usually in old casinos often so that way it can attract a lot of users, I always win a lot of money on demo mode but that's their marketing system to attract attention when they are awarded a big win in demo mode will usually increase their confidence to gamble and make deposits.
Gambling with high self-confidence because you can beat the casino in demo mode will make someone want to gamble with real money but in fact they will experience a losing streak with high stakes so that at that time the casino will destroy the gambler's confidence then win big and the gambler will continue curious to play again and again until you go bankrupt.
Is it true, that not all casinos have a demo mode? because as far as I know, this is a feature provided by the slot provider, so when a casino adds slots from a certain provider, it will immediately come with a demo, it is no longer the casino's job, because as far as I have ever played, even in very new casinos because I want to catch the bonus, then the demo mode will be available in the slot game.
I don't know how many discussions there have been about demo mode where players often get very high multipliers, but when using real money the results are very inversely proportional, and in my opinion, it's not because there is a difference, but more because in demo mode players can play as much as they want until the end hit a high multiplier because the funds available there are unlimited, whereas with real money players will start to worry when the funds are running low but have not yet reached the expected multiplier so they start making decisions such as stopping playing or changing slots or other games.