What if a ruling requires information held by someone else? Should the case just be dismissed because of lack of evidence? Having a functional justice system is probably worth some snags.

The legal cost aspect is unfortunate. However, as others have mentioned, the court probably doesn't require the assembly of new documents, but rather submission of existing ones. So while there is a cost, it's not devastating.

The interesting question is whether or not this specific subpoena has real merit, or if the court was played by Meta.