We used to send them tons of traffic and I recently saw something, which reminded me of how unreal the whole "thing" was... two players of ours alone deposited more than 400k USD and our commission was a whooping 2.5k USD...

It’s interesting how they let this opportunity slide since you can gave them steady traffic with good wager volume in long term and decided to cut you out just to save on affiliate commission. Commission percentage is just small in comparison to the potential they can get on players with high bankroll given that all casino games work in favor with the house.
Does your players still play in the casino? I think they are confident enough that players that you brought is already playing with or without you since they are already registered and invested enough money formtheir account level.