I think the more likely cause is you said you started at a regional in 2010 and left after a year. You now have 1200 in a 737. So ~600 hours at the regional plus the 1200 is only 1800 part 121.

Unless you were prior military or started at the regional with 4000tt I'd say your experience is why you aren't getting called, not the line check.

If not...like others have said, I wouldn't sweat a single line check failure.