who can tell me why the pending time of I-485 of EB1 and NIW is

As I know, recently, if somebody s the application of I-140 and I-485 in EB1 case, After his/her I-140 is approved , his/her I-485 also is quickly approved. However, many guys , including me,got I-140 in about two years ago, but I-485 is still pending . Why? I don't believe this is the reason of FBI name check. Who can tell me the main reason that cause the significant difference of I-485 between EB1 and NIW.
Thanks a lots!