I agree with you but you shouldn't forget that most viewers of this kind of videos are very young and one part of them is not adult. Then there is a need to find a way to prevent them from being abused by those scammy/fake demos.
And this is the problem, if the audience of those kind of channels were people that knew that this kind of promotion is not real then there will not be such a huge issue, but many of those watching that type of advertising are people that do not have the experience necessary to know that what they are seeing is not real, and since they trust the streamer they try their luck in a casino due to that publicity thinking winning is as easy as what they saw in the video only to realize too late this is not the case.
But the fact is that everyone has a different curiosity and personality, of course, so even though there are people who realize it's not real, the fact is that they are sometimes also compelled to return to betting because the video is like a motivation or encouragement for them. Also, those who are affected do not always have to use the same site or platform, at least when they feel the video can be an encouragement then they will easily make a deposit on the platform they are used to. Therefore, they will roll with high confidence and with the hope of winning big or easy like the video they saw. Even though behind all that if they want to win big, they must at least learn it first and not only hope for luck.