The main thing getting Kalshi all the attention from the states is their sports gambling markets. Not sure if polymarket offers those to US.
There are 3 separate reasons WHY states are so strongly opposing Kalshi's sports gambling: 1) Kalshi is doing it in a way that avoids state taxation, licensing and regulation, 2) the online sports gambling companies spending billions on TV commercials don't want untaxed, unregulated competition, 3) The major sports leagues are concerned it will undermine the integrity of the 'product'.
Of course, there's no material difference in actual harm to the public between Kalshi sports betting and Online Sportsbook Apps, they both enable gambling addicts, cheating, etc. The hardball reaction is about ensuring Kalshi sends tax, licensing and lobbying money to each state government. The sportsbooks have spent billions ramming gambling legalization through and don't want Kalshi getting a 'free ride' on the bus they paid for.
Even the sports league's opposition isn't as pure as it appears. While they don't want players, coaches or referees to undermine game outcomes, they also sell exclusive access to real-time on-field data feeds to sportsbooks for hundreds of millions of dollars. The TV feeds we watch at home are ~8 to 15 seconds delayed. Getting the real-time outcome data from every pass, kick and run in 800ms vs ~8s on TV is worth hundreds of millions to online sports apps because it lets them front-run real-time bets. When people at home make real-time prop bets on the next play, many times the company already knows the outcome. Something to remember next you hit "Bet" on a real-time prop and get a spinner saying "odds updating" and then "bet expired". It might be because your bet was going to win, while if you'd taken the other side, it would have accepted the bet and taken your money. Yeah, that's against the law in a casino but not in an online sports app. Right now, those apps being "Regulated", mostly means they're paying taxes, licensing fees and following "Know Your Customer" policies to minimize money laundering and minors gambling. Actual fairness of the bets doesn't enter into it any more than carny midway games. Consumer bettor's job is to consistently lose, while only winning a little back often enough to bias selective memory and keep them interested. Anyone who actually wins too often on bets that are too big, quickly gets their acct capped to $1 bets.
Note that Polymarket's non-US business is crypto blockchain whatever so ... good luck with that. The ability to get your money out could disappear at any time and as far as I know there's no recourse if they just decide to screw you over. Not that CFTC is super effective but it is something.
So is Kalshi. The entire question is how the CFTC made up the authority to regulate gambling out of statute that only ever mentions exempted commodities.
Also, more to the point, Polymarket actually does have at least three active lawsuits against it.
edit: looks like this has something to do with it:
> Kalshi has been a CFTC-regulated exchange since 2020. Polymarket exited the US in 2022 after settling charges with the CFTC, and only came back after buying QCEX, a CFTC-licensed exchange, in late 2025.