There are plenty of Facebook/mobile "play casinos" which produce a fair amount of revenue by not refilling the customers' "free chips" fast enough to be fun so people will pay for more.

There's also a bunch of fun dark patterns (side currencies, battle pass and leaderboard features, and account evolution you need to play X amount to unlock different games, and once you've played that much you can no longer scale down to very low wagers to make the free tokens last longer.)

At least Genshin Impact has a fairly high quality game with some play value attached to the shitty casino.