I don’t understand why the streamer can’t participate because most of the times the terms clearly state that casinos employees, and their families can’t participate, and a streamer is not an employee. -snip-
"it depends".
A streamer can actually be considered an employee of the casino, especially if they get a free stack to gamble with during their livestreams. In such a case, I think it is obvious that the casino does not want this player to participate in the contests. So he would potentially win the contest with "free money", which surely misses the point of the contest.