Have you read Bernstein's book? (See title in my signature)I'm not sure I have the answer to your question just yet but I think it's because I've been on oral meds for about 14 years now and the last 3 years glucose readings have been steadily rising and I've been very ill.
I only discovered low carbing since joining here, a few weeks ago, it's not easy but I'm working on it.
Going onto insulin....Its a trial... I did discuss with the Dr, that hopefully to avoid putting on more weight, I inject low dose of insulin and stick to healthy lifestyle of eating and excercise to reduce the weight.... I don't know if this'll work...Only time will tell.
Also I'm so desperate to come off gliclazide as it's causing terrible stomach problems
He has wonderful results combining low carbing and small amounts of insulin or other meds, precisely tailored to the individual. It's a great book, and very inspirational.