I think ads play an important part here. They go into unknown casinos despite the reputable ones already there. They've just clicked and seen it from an advert that they see while browsing the web. I'm not also gonna risk some money there and if there are people that say that it's a legitimate one and they've just used it then that's a good review for OP to have a reference since that's what he's looking for. But as for me, I don't want to get into the casinos that I don't really know.
Same here, There are actually scam casinos who are doing advertisement here which is the well known 1xbit. They pay good to their campaign members compared to other signature campaign but at the end it is a mere scam casino that is trying to lure gamblers here which isn't effective in my opinion. There are a ton of thread here that is asking for legitimate casino, It is easy to browse that and make it a reference in choosing a casino. I would personally choose the proven and tested casino compared to the ones who are a bit shady but offering a alluring promotion.
That's a proven method for those that are looking for a good casino, they just have to find the ones that have been proven and tested by many gamblers and by the community.
Those ads that are appearing, not just in signature campaigns or bounties, they're easy to be seen by those gamblers already who have visited other casinos as well as the newbies that have been searching for one. It is the algorithm of most search engines these days and they'll be targeting you and sending you more ads about it.