Unless ~800k users cancel it is still a net positive for them and that is with the current relatively small contract they have. The reality is that money is in B2B.
According to QuitGPT[0], as of now, 2.5 million people have done so, which they base on "website signatures, share counts on social media, and credible app usage data". I don't know how accurate this is, but seems a bit of a high number.
[0] https://quitgpt.org/