Title is misleading. They made a FOIA request some time ago, and these agencies haven't responded. The lawsuit is simply a way to force the agencies to respond to the request they already made.

ref: https://www.aclum.org/en/news/aclu-massachusetts-files-lawsuit-seeking-trump-declassification-order

I don't know why they initially made the request, and it's not important. But Federal agencies are legally bound to respond. They cannot be allowed not to.