Collusion to move markets is against the law.
The assumption is that hedge funds do this all the time, but without evidence of collusion it will never stand up in a court of law. Hedge funds also have the legal resources to fight such a case.
On the flip side of that, participants in Reddit thread recording the intent to collude to move the markets are also recording the fact that they intended to break the law. They may delete their posts. They may conceal discussions in private chats or e-mails, but none of it is removeable, and all of it is discoverable.
So I think we will see examples made of the people who broke the law. Prison time done. Homes taken away from families of the conspirators, etc. You have people who have not thought about the consequences for their families and their children who have taken actions that could result in their families being destitute.
In order to restore confidence in the market, they have to make examples of these people and terrify any future conspirators in such schemes from doing the same. They have to do this or risk seriously damaging the stock market and all the financial institutions that underwrite the companies in the chain of custody.
The can also just not pay out on any of the investments. The majority of these investors are not bought any stock at all. They do not actually hold any shares in the companies at all. They just think they do, but as novice investors, they don't actually understand how the stock market works. So they lock them out of selling their positions 'pending judicial review', leek rumours that the platform is in financial problems, let other stock holders close out their positions and move their investments elsewhere, and then file for bankruptcy leaving the locked in investors with nothing but a claim against an insolvent company. They never owned any shares in GME anyways.