I am always very surprised when some people said the gambling sites are not having provably fair games because if they have the provably fair games, they will still be winning. What casinos only need are customers. You have already said it that the gambling sites have house edges which is enough to make money from almost all their customers.
The problem is that for some casinos, the house edge is not enough, or is enough for a business point of view, but not from the owner's point of view of getting rich quickly. IN theory provably fair system should mean no cheating depending on your bet, in reality is harder, we have already had enough cases of
- fake RTP, being full percentages way below what is advertised
- casinos using pre-determined seeds as default for clients
The game is still fair, but you're not playing with a 99% RTP but 90% and your seed is already making you lose more than average.