There’s a lot more to read about it than Wikipedia. The animal sourcing is unreliable too, those farm animals don’t make it, they get it from being outside and eating from the soil and drinking from various natural water sources. That doesn’t apply to most animal-based food products as those come from factory farms, which is why they supplement, usually as multivitamins. Those who aren’t eating a plant-based diet are essentially consuming second-hand supplements, along with second-hand amino-acids, second-hand lipids, second-hand calories. And B12 deficiency is pretty big in many human populations, especially among older adults. Everyone should be supplementing, really. You should stop making it sound like it’s difficult or disgusting, it isn’t.
Maybe I wasn’t clear, but you certainly have a lot more reading to do. You have a first year student’s understanding of the issue.