Maybe in jurisdictions like the US, where the copyright lobby has been very effective in getting aggressive anti-piracy legislation with huge penalties enacted, the statutory damages alone could be astronomical? Since Facebook could still afford to pay them, it might also offer to settle for a very worthwhile sum without even the risk of going to court.
I'm generally not a fan of hugely disproportionate penalties for copyright infringement, but this isn't some normal person falling victim to opportunist lawyers engaging in a form of barratry, this is a huge company with its own legal team who should know better than to wilfully infringe copyright.
They could potentially have ... friends ... who would have an interest in seeing a case brought, though.
(And since Bollea, barratry seems acceptable.)
Perhaps, but sadly, I don't actually foresee vendors wanting to exercise that right. From a business perspective, why bother?