good question, and indeed in some MTD they argue that

" The Defendants also argues that the government has not refused to adjudicate Plaintiff’s adjustment application altogether. Rather, according to the government, the adjudicative process has been delayed due an ongoing investigation, such as waiting report from FBI, transfering to local center for interview ....."

they are some already some good arguements to fight back this kind of question.

In short, most of case, USCIS should be on the defendant list