Although they are all bigger or smaller scams, they all survive because their customers are either mentally incapable of spotting the scam, gullible, naive - or suffer from gambling addiction. They all manipulate, that's their very nature and sole source of revenue.
Do you have any proof for this? My friend plays on Prime-dice every week or so. So far, he hasn't incurred any loses at all. I have studied the results from hundreds of games played by him. I found nothing suspicious.