Peanuts are legumes, like peas, but present far more problems with allergies.
Eggs are far more resource intensive to produce than peas and also present ethical problems (e.g. what to do with male chicks - throw them alive in a grinder or suffocate them?). Cow production has similar issues, like water usage.
I’m sure they could deal with it in a better way than they do, ethically - but they’re operating under the restraints of capitalism, which says compassion is too costly.