And why only Meta? Google's YouTube is brimming over with scam ads. Google is even more liable because it's not simply providing a platform where the scams are posted as content; it's taking money from the scammers and placing their ads.

Google does so knowingly. People are reporting the ads via the provided workflow and describe the scam. Yet the same scams persist. In spite of being informed about scammy advertisers, Google takes their money.

I would say that Facebook do have a valid point if they say that they are not liable for posted scammy content, even that content manipulates their algorithms in order to reach users. Google do not have any similar such defense.

Because that's the way courts work. This court only had jurisdiction over Germany. It is possible that other courts with broader jurisdiction would rule similarly, but someone has to bring the case.