The question you need to ask is, whether these casino's are spending money advertising to individual users and influencers. Some of the big casino's are sponsoring major sporting events and they might promote their casino with influencers who are genuine gamblers and they might have a separate affiliate deal rather than shelling out money on a daily basis .
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When it comes to casino advertising it is always on places where gamblers show up, and read updates You don't need thousands of groups or platforms

If a new casino launches it only needs influencers an announcement thread here, a signature campaign, and a good affiliate system to generate leads and from there maintain its reputation, You don't need $6.2 million daily the initial campaign will only cost a few thousand dollars and building a reputation is equal to million dollars.
I doubt if even the top casinos spend $6 million for their marketing campaign.