While it’s true that many (most?) people won’t have a problem, a minority have their lives ruined as well as family members, and the risk of that is reason enough to regulate it.
First, most states ban many forms of gambling...so I would call that heavy regulation. Second, whilst the regulatory approach in legal states differs - for example, NJ...for various reasons...is one of the most strict - the overall level is high.
Most states have self-exclude/no-market lists, most states require links to gambling addiction helplines in adverts and within product, responsible gaming features are required in every state de facto (and providers are going beyond this in reality) so this is deposit/wager/loss/time limits, reality checks have effectively become mandatory, some states have hard limits on total wagers or require ACK over limit, deposit alerts are also moving to mandatory, there are limits on some kind of machines and how they operate (this is a massive difference to casino gambling, IGT designed physical machines that only appealed to addicts, that experience can now be 100% controlled online), etc.
I don't think people are aware that state regulatory bodies exist and are doing a huge amount. If you compare with European countries, I would say that providers are probably more aware of their responsible gaming function (afaik, many providers have responsible gaming goals that impact board-level compensation, so in the past year you had providers blanket limiting customers based on certain categories...which, I will add, is not an ideal approach, no regulator asked them to do this). In addition, there are some aspects of regulation that, afaik, don't happen anywhere else: for example, most state regulators are checking code that providers are deploying to ensure it is compliant.
This change in regulatory approach is largely a function of things moving online. To be blunt, when Adelson died then the old approach of functionally limited regulation was over because no-one was being paid to advocate for it. Online gaming also enables far more controls over the experience i.e. you can enforce hard limits (as opposed to a pit boss telling someone to stop). I can only assume that most people are completely unaware that this is happening though.
The difference with Polymarket and co, which are regulated as financial firms, should be quite obvious too. People are gambling on their site, they are doing none of the above.
This isn’t all that different from alcohol.