My rule of thumb is that if the streamer is big enough and drives enough attention, there must be any kind of sponsorship going on to generate income.
I mean, most of the channels on YT that never received sponsorships nowadays do and there is a good chance the advertisement departments of the biggest casinos are always looking to expand their ads.

Also, I usually do not watch videos of people getting very lucky and winning millions, would only feed my greed and expectations for money. Not my favorite thing, but it is mostly personal.