You can be sure that influencers get paid a lot of money to promote big gambling sites. Whether it is allowed in advertising on youtube itself, I doubt that. You often see that indirect advertising is made by broadcasting certain matches where you then see on the billboards that it has been made possible by certain gambling sites. That is also a form of advertising. And we all know that online marketing is very powerful and the gambling industry is billions in that. I think many people do not consider the kind of amounts that are offered to advertise on certain gambling sites.