It isn't. Hedge fund managers have "idea dinners" with dozens of their friends all the time to discuss what plays they are thinking... they frequently also bring in guests that represent companies, or even politicians/former politicians to discuss lobbying strategies to keep this exact type of collusion and market manipulation legal for them.
But as soon as a bunch of the dreaded "retail investors" start doing it in the open, Wall Street calls on K Street to save them.
That's amazing. So they basically found a legal protocol to do things that would otherwise be illegal, and institutions like judges and the SEC just let that happen?
This would be illegal I think.