I don't remember the reason Treasury got booted as a defendant
It's a contract claim. Treasury isn't party to the contact between FHFA and shareholders.
EDIT: Actually I don't know if this is the case or not. Originally I thought this was shareholders suing the GSE's over the contract rights of their stock certificates, and that FHFA was simply a stand-in for F&F. But I'm gonna have to reread the filing.