If I made a platform like that, I'd be RICO'd after the FBI kicked down my door and confiscated everything I own.

If I had the connections Polymarket does, well, then we can just place bets on when people will die, everything will work out just fine and the President will invest in me.

If you don't mind not having US customers, it's easy enough to get an online gambling license in a few jurisdictions, maybe $20-50k all in (Nevis and Anjouan are a couple of the more notable ones), at which point you can serve a large portion of the world. This was basically the scenario polymarket was in for awhile until they started making inroads into US regulatory apparatus.