They made a business decision to move on from this content platform. I love to hate on facebook with the best of them, but they really don't "owe" anyone anything.
There seems to be this pervasive attitude in technology circles that platforms "owe" other businesses and individuals something when they build businesses on top of said platforms. Just because you spent 54MM in ads on a platform doesn't entitle you to anything when a legal or business decision has to be made. Is it crappy not to communicate and give an explanation...? you bet it is. Did that 54MM in spend generate anything for Shared... you bet it did. Everyone was a winner until Facebook moved on.
I suspect that Facebook and Shared working to negotiate out of this will just result in a lot of spinning wheels, ammunition collection on both sides to pursue legal remedies, and nothing of real value changing. Facebook said we're moving on. Done.