My guess is - legal or not, Facebook might’ve calculated the consequences (aka, fines) and decided it is worth the cost. Most publishers will not have the resources to fight them in court anyways

Most publishers have resources - it is millions, but it looks like a cut an dried case that they are highly likely to win. A 2 $million investment that results in $10 million dollar is a good investment. The numbers seem reasonable, though of course publishers need to consider their real situation.