>Why is asking users for consent, a key piece of GDPR compliance previously, suddenly not OK?

Asking for consent is still OK. Just the way how IAB has been doing it is not OK as it was found to not constitute explicit consent.

And before you say that explicit consent is not defined there are easily accessible guidelines from the European Data Protection Board. https://edpb.europa.eu/our-work-tools/our-documents/guidelin...