You need cows to produce all of that just like you would meat. The way cow physiology works requires that calves be birthed periodically to maintain milk production at large scale. The dairy industry is to a large extent, a by product of the meat industry. Those new calves have to go somewhere. And you have to keep in mind that 70% of the world's population is lactose intolerant as adults. They rely on nondairy meat products for the majority of the B12 they get. OR you switch people to vegan substitutes that have B12 added to them. Right now those are niche/luxury products which is problematic for developing nations. Like... imagine going from small scale cattle and poultry farming to relying on B12 bacterial fermenters and soy production at large scale. That might be doable if new processes for using certain strains of B12 producing pseudomonas bacterial cultures can be developed for fermented soy products like tempeh can spread there but again, those arent there yet. More R&D is needed.