You said it right.. same type of platform, but one is regulated while the other isn't. That said, I think the non-regulated ones are still more popular. A lot of bettors prefer prediction markets like Polymarket because they don’t have to deal with KYC requirements.
I think I have heard before that those that are living in the United States must have to pay tax if they win while gambling, and it is not a small amount of money if the person win big. No KYC on Polymarket. That can make them just decide to use a noncustodial wallet to connect to the prediction site and bet instead of using the regulated one with license. That sounds not good at all but I know how people think.