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.
Maybe it's true that streamers can play with piles of money with regular games and this is only done when streaming live so I think that other players will be suspicious if the streamers join this contest participation.
I think that streamer with live players has also been profitable with a pile of free money so participation is not enforced by him.
And this is only used for ordinary players, we might say regular players with contests being contested, but this is just my opinion if it's not allowed for streamers.