Why cheating discussions aren't not allowed in the forum ?


Because talking about online cheating is taboo and undermines the whole game.
Why would players keep paying for a game that they know the players can't be trusted and the odds are stacked against them?

...or, maybe it's FLAMING. I hate cheating as most other players do too, but DOXING individuals inFLAMES hostilities. You can't name call in virtually ANY forum. Sometimes laws protect the rights of the guilty. That's the price we pay to be protected from trolls. Everyone has the same rights.

it's been a rule since 2007, if u got a problem with a cheater, report it. and the Cheating forum is where u post that stuff anyways

The main problem is that a lot of topics get posted about members cheating where there is not cheating happening. Those type of topics attract accusations, some valid, some not and the site doesn't want members to be publicly accusing other members.
There is a mechanism on reporting members and that is what should be used.
https://support.chess.com/article/209-how-do-i-report-someone
For more general discussion on the issue, the following club is available: https://www.chess.com/club/cheating-forum
You still can't make public accusations there but can have discussions around it.

Also, the site doesn't pretend it doesn't happen and has an article and reports on the closures each month:
https://www.chess.com/article/view/online-chess-cheating
https://www.chess.com/article/view/chesscom-update-october-2023#FairPlay