It's all because of money. They're certainly sponsored or paid for doing so. Thus who can't resist if the offer is too good? It's quite normal nowadays. These streamers are attracting their viewers to also gamble on the specific casino. Because this kind of promotion is one of the effective way to lure many people to play.

Seeing someone to win huge is really tempting to try it for yourself. Although it seems these streamers lost their dignity for not even thinking their minor viewers, but that's how it is when it comes to money. They're paid so what can you expect.