But the untrustworthy ones end up scamming their customers, or at least playing dirty tricks, like letting them bet from a country that is forbidden in their ToS and only when the user wins and is going to withdraw the money they ask for a KYC to deny the withdrawal because they have broken the ToS.
This goes beyond online casinos. Most brick and mortar casinos will use the same tactics. They see some underaged kids go in, but as long as they don't win anything worthwhile, they ignore it. But if that "unlucky" kid gets something big, then it's "give us your id" time, and the kids usually run away.
Neither of them, online or real ones should do that, as it's immoral