Correct.
But nobody is enforcing compliance.
So they can just keep it on American servers and sell it to OpenAI or share it with the US government.
Also, there are a lot of bots copying everything on reddit and other sites. Even if reddit would comply with GDPR, these bots cannot be traced and cannot be fined.
Because they manage to attract investment.
As long as investors are willing to give cash in exchange for equity, a company can operate on that cash and run at a loss.