..... Even I485 folks can stay and work in this country while process pending...
That is one level of comfort . But then the discomfort becomes one is stuck at the same job for 5+ years without much promotion. AC21 can be tricky at times. Don't want 5 years waiting go down the drain.
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But you should understand that primary role of government (USCIS in our case) is to protect people of United States ....
So it is in their best interests to quickly complete the namecheck.
I am sure most of the cases are sitting in FBI shelf for an agent to look at or to transport some paper files from a field office. A resource issue as stated publicly by FBI at their FAQ page. Otherwise how the long pending namechecks get resolved in weeks following expedited request from USCIS ?