Insulin resistance is caused by leading a lifestyle where you are constantly spiking your insulin levels through diet, lifestyle, genetics, etc... Like any hormone or steroid your body develops a tolerance and you need to increase the dosage to have the same effect while also increasing the side effects. Everyone who eats carbs has some level of resistance not just "diseased already".

A typical Irish or Russian diet without meat is fine by current norms but not optimal. Eating a veggie burger with fries and milk is not a great diet though.