This is not an instance of regulation being unpredictable. A plain reading of the GDPR makes it pretty clear that it is illegal to require consent to data proc

This is not an instance of regulation being unpredictable. A plain reading of the GDPR makes it pretty clear that it is illegal to require consent to data processing for targeted advertising as a condition of using a service. I'm not a lawyer or a GDPR expert, and I knew this. There is zero chance Facebook didn't know that was both the intent of the law and how courts were ultimately likely to interpret it. They decided it would be profitable to interpret the law in an unreasonable, but semi-plausible way that allowed them to increase their profits. Of course they hope they can convince the courts to accept that interpretation permanently, and I'm sure they've weighed the probability of that against the amount they're likely to be fined.