I'm pretty sure Facebook has the resources to have hired competent lawyers to advise them on that, and the money to afford preparation and execution of a strong court presentation of their viewpoint.

And Facebook probably had more information on what is necessary for the system Facebook provides to work than people trying to guess that from the outside.

It is, of course, possible, and, perhaps even likely, that a court will disagree with what they argue, and force a change—but it may be, from a PR perspective, worth the cost of non-compliance sanctions to have any decrease in utility resulting from changes they will be compelled to make to be very visibly forced on them by orders that they vigorously fought rather than self-initiated, so that European authorities and the GDPR get the blame for any reduced quality.