Well, it has something to do with acting in good faith too. Not respecting GDPR because of an oversight or even laziness is likely to be met with warnings.

But blatantly violating it on purpose (this is no question: these companies have specifically claimed they implemented these obviously non-compliant processes because of GDPR) should not warrant any goodwill on the part of authorities.

the point of “no instant fines” is to give companies a chance to change and develop their GDPR systems. if those systems are both complete, and in violation, why shouldn’t they be fined?

That is yet to be determined by the regulator and the courts. Facebook has made their changes. Now someone will complain to the regulator. Then the regulator will make a determination and maybe ask Facebook to make further changes. Then Facebook has another opportunity to comply. If they refuse to make those changes they will get fined and can go to court to fight the regulator's decision.

At least that is my understanding of how this system works.

But there's a deeper reason why the EU fining Facebook would be a deep demonstration of malaise, incompetence and greed. From the report:

Research has shown that most users will never look at, let alone change, the default settings.

That's right, and you know why? Because users don't care and never did. This entire privacy crusade is made up out of whole cloth, by the EU, to obtain power and money. These foolish governments constantly demand more and more controls, consent agreements and so on and the users constantly don't use those new controls and always consent because they were perfectly fine to begin with.

There are no dark patterns. There are no evil conspiracies. There are only users, who enjoy broadcasting every detail of their lives to their friends and sometimes the world.

FB is being malicious, same as always. hopefully they'll get smashed by the fine when they continue to resist the law.