You should always do your research, even if the streamer advertises a reliable and honest casino. The problem may be that, for example, he is from country A, in which the advertised casino has no problems, and you are from country B, in which the casino has problems/restrictions for citizens of this country. Thus, if you do not check the compliance of the casino just for you, you can get into an unpleasant situation.
The biggest gambling streamers are making millions of dollars from advertising certain casinos. When you're getting that kind of money there is no incentive to telling people about the negative aspects associated with gambling. They just want to keep the money coming in. In all fairness, it's the user's responsibility to read the terms and conditions before making a deposit. People should always be under the assumption that streamers are there to provide entertainment and what you see is not an accurate depiction of real life.