The government needs mindshare and advertises just like any other entity. Just like people use Facebook to tell people not to use Facebook, the FTC may buy or use services from companies they are taking legal action against. That's not an endorsement of the practices they are fighting against; it's simply how businesses work. Facebook is where the people are; if you want people to hear your message, you take the message to Facebook. It's especially relevant in this case since their work directly benefits Facebook's users, so it would not make much sense to not have their message heard there.
Also, they settled and all is good between the FTC and Facebook.
Also, they settled and all is good between the FTC and Facebook.