It's one thing to do a paid promotion through a promotor... but to lie and act like it is their own money they are gambling with.. It's not only immorally wrong, it's possibly illegal depending what jurisdiction the streamer is in.
As long as they are not saying it openly they are not commiting anything wrong from the legal perspective but it can be immorally wrong but why does someone choose to spend their money because they saw a streamer is making tons of money by doing the same, which is actually greed driven activity right so those streamers are using the people's greed to make money for them.
They can lie to make money, all they care about is the legality, as long as they are safe on the legal side they can do what the promoter would like them to talk and promote, that's why it's hard to trust those who are promoting online, I would still prefer a forum like ours as we can see the transparency we are looking, no bias opinion will prevail and etc.