From memory, the issue is publicly disclosing CPM among some other things (at least it was 4+ years ago).
I actually wonder if posting it off-platform is even allowed, I've seen Twitch enforce their platform exclusivity for 24 hours for Partners.
The same logic applies to most tech jobs. I would expect more big tech companies would want to broadcast their comp numbers to encourage more people to pursue those careers and apply to those companies. The average joe probably assumes SWEs at Google make $100-150K MAX. If more people knew they could make doctor-like numbers without going to grad school (or even going to college at all in some cases), more people would go into tech. But I guess companies have done the math and determined its better to conceal that information best they can to keep their advantage during negotiations.
[1] https://www.youtube.com/watch?v=3Rm-ElJPDJk