If you have been adherent (very low fat, WFPB) and are lean....you may be insulin sensitive but not have enough insulin. Some people develop latent autoimmune diabetes of adulthood, aka diabetes type 1.5. unfortunately some people have genetic tendency or have been exposed environmentally to triggers that induce beta cell death over time. There are also microbiome differences in how your body responds to micronutrients as well as factors that influence insulin signaling and release (mutations in melatonin receptors, etc). Long story short, as a society most T2DM are insulin resistant, but there are people where the problem is insufficient insulin.
https://diabetes.diabetesjournals.org/c ... etes%20(17).
I would ask your doctor to work you up for LADA, if your beta cells are indeed failing, then recognizing that sooner than later is important. I have a friend with LADA and she does inject insulin, but still follows WFPB diet as makes insulin dosing more regular and the diet so healthy. She does watch simple sugars and always goes for the high fiber complex carbs over things like white rice or pasta.