I think as well it's with considering the normal order of testing.
From my understanding the c-peptide test is used to help diagnose Type or otherwise confirm diagnosis *after* there is reason to suspect someone is diabetic - often following an abnormal Hba1c test.
It is not used to diagnose diabetes in the first place. That is what the Hba1c test is for.
If your Hba1c tested by your GP and showed a result of 34 (well anything under 40-42) they would not send you for a c-peptide test as you're not diabetic.
So constantly having your c-peptide tested when you're not diabetic isn't really going to tell you much.
Cheeky edit - and if your c-peptide was a bit out of range they'd do your Hba1c to check whether you were diabetic or prediabetic. Which, at the moment, you most assuredly are not...