Nit: b12 - until the late 90's (I think) when it was discovered how to be made in a lab, there were no non-animal sources of vitamin b12. Organs are also full of vitamins, but most people don't eat those.
Most Americans don't think they eat organs, but they are a big component of most processed meat foods, like sausages. But offal consumption is prevalent in the rest of the world. Even in the US, you can find offal in many Mexican restaurants.