Kalshi has about 89% market share among regulated US platforms. They have a lot to lose if Congress decides prediction markets need the same treatment as securities. Suspending candidates who bet on their own races is a cheap way to demonstrate they take integrity seriously.
The interesting question is whether self-regulation is enough. These three candidates were caught because the bets were on their own races, which is easy to detect. The harder problem is friends, family, and staffers placing bets based on internal campaign data. That pattern is nearly impossible to catch without the kind of surveillance infrastructure that the SEC uses for stock trading.
Betting on themselves losing would be a problem, since then they could manipulate the result by sabotaging themselves. But that only works one direction.
Win: get the salary in congress.
Lose: get money from kalshi.
The problem with sabotaging yourself is that it challenges the assumption that everyone is playing to win. If anything, supporting other candidates might be questionable, if you bet on yourself losing.