Or they're not grossed out at all. They just make the rational decision to not consume dairy because of the water, energy and food consumption of the dairy/meat industry. Or because of the greenhouse gas emissions.
What are you saying, if you don't want to contribute to the things mentioned above, you shouldn't be allowed to drink anything that remotely resembles cow milk?
That's exactly why it's milk actually. Just like coconut milk, which has existed forever, milk of magnesia which has existed since 1875, and soy milk which has been widely consumed since the 1800s.
Oat milk is not milk. But it's milk. English has no problem with that. Pizza pie is not pie. Boot camp is not camp. A house boat is not a boat. We understand each other just fine. You add a word to another word and you get a third word that's unique from both of its parts.
There's a similar push happening in Australia.
BTW, I think pizza is only called 'pizza pie' in the US? And a house boat is definitely a boat if it floats.
I can't explain it, but milk is just gross to me. I eat almost every other dairy product (okay, I'm not a fan of something too fermented, like kefir, ayran and such), but plain milk is psychologically repulsive. Maybe it's because my grandma had a cow when I was a child, and seeing milk come out of a cow was disgusting. Processed dairy products are kind of too far removed from a cow in my mind, so they're okay. Maybe it's the smell of country milk. I don't like homemade country cheeses because of the smell as well. For this reason I love oatly, and almond and coconut milks. Soy milk is fine too. I can also dring flavored milks or coffee with milk (although I prefer it black). I've only met one other person like this in my life, and it felt very validating that I'm not alone in this.
As for why, it's the same reason people make substitutes for a lot of things. I have coeliac disease and cannot eat any gluten-containing bread, so I make substitutes using various gums and binders to replace the gluten. Even though it isn't the same as a gluten-containing bread it's still useful.
Same goes for alternative milks. An emulsion of fats and water is a useful substance even if it doesn't come from an animal. It binds tannins in tea and coffee and has a nicer mouth-feel than plain water in breakfast cereals.
Not sure what the original etymology of "Milk" but it seems to have evolved from just referring to mammary liquids to liquids of a smooth, translucent or opaque consistency, e.g. Milk of Magnesia.
I always use dairy milk for coffee and found it odd why people would use soy or almond milk. I guess both have fat; do plant fats react to coffee in the same way that dairy fats do?
Anyway, I pour almond milk on cereal because I like cereal. It probably wouldn't be great on fruit loops, but it works nicely with granola and other nut based cereals.
A good discussion about this: https://cooking.stackexchange.com/a/76006