Milk

Maybe because somewhere close to 70% of the world's population can't properly digest/absorb lactose after infancy. That, and people are often highly skeptical of commodities that have a massive lobbying/marketing presence. Personally, I don't drink milk (still consume butter and cheese) because it does not make me feel great. It bogs down my gut and causes breakouts. More on reddit.com

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There has been, kinda sorta. The process is just too expensive to be able to sell it as "milk", so it's being used in higher sale-price milk products like ice cream. A company called Perfect Day uses fungus to create the proteins found in cow milk, like whey proteins and casein. Their ingredient was used by Brave Robot for ice cream sold in stores, and Smitten in stand-alone ice cream shops. More on reddit.com

I believe there's a few nutritional differences between human breast milk and cow/other animals milk, if I'm not mistaken More on reddit.com