It was mentioned previously, B12 is a bacteria. Modern lifestyles and agriculture leads to less exposure to bacteria, thus less B12. B12 isnt produced in animals or plants, its solely synthesized via bacteria. Its common practice in the meat industry to inject cattle with B12 supplements, which are vegan, one way or another you are taking a supplement. Modern agriculture has also lead to decreased nutrient quality of food, thus a reliance on supplements to some degree is needed. Visit a nutritionist and get your blood checked, I can almost guarantee they recommend supplementation.