Makes sense. Why would a newspaper chain with ethics that are often questioned by readers volunteer to be challenged by a body that investigates reader complaints?
Forget the "political correctness" canard. This decision is economic. If you're losing money all the time, withdrawing from a regulatory body--even a weak one like the press council, saves you on legal fees. And if your goal as a newspaper chain is to slander and spread hate-speech, the savings can be considerable.
There's no glorious rebellion here. The same newspaper chain that is rumoured to make its own employees take out their own trash and pee out an eight floor window rather than provide functioning bathrooms wants to cut a few $s that it might otherwise have to pay to their lawyer squad.