Because they're not knowledgeable or consenting. You don't know your odds, and the house makes sure of it. And if you're addicted, you don't really consent.

Exhibit A: Tobacco. Prior to regulation, it was advertised widely and thought to be not that bad.

Once we regulated knowledge and consent, use plummeted.

For knowledge, we display pictures on the pack and carton of people in agony dying of lung cancer. We tell them the odds. For consent, we mitigate by saying "WARNING: nicotine is an addictive chemical. Nicotine can be more addictive than Heroine".

The fallacy here is that markets are naturally free and government intervention makes markets less free. That's rarely the case. Often, intervention makes the market more free.