They're idiots. Some believe it's because pasteurized milk had added chemicals, which isn't correct, pasteurization is simply heat. But idiots will be idiots.
For others it's the general anti-science/education bullshit going around now. The crossover with the anti-vax is nearly a circle it seems.
"I'm going to buy the least healthy version of the least healthy kind of milk." —Folks concerned about their health
I genuinely feel bad. It's like they're so close. Going out of your way to care about your health is good. Challenging broad societal assumptions is good. It's just that this completely fell apart when they arrived at the "now weigh the sources critically" stage. The charlatans who sold them this idea for profit should be in prison.
Idiot conservatives (and many 'crunchy' people who don't realize they are idiot conservatives) believe raw milk has more nutrients, that its better to be exposed to more harmful bacteria because that will build up your natural immunity, and can prevent you from developing asthma and allergies.
But none of that is true.
Raw milk has no more nutrients than pastuerized milk.
The 'crowd exposure immunity' approach just results in needless deaths and suffering, little to no functional natural immunity increase as bacteria variants evolve too fast, as well as providing more vectors for viruses in birds and cows to jump into humans and then mutate to spread from human to human, a potential pandemic.
And raw milk consumption has no effect on liklihood of developing, nor treating already existing asthma or allergies.
I remember reading a book that was illustrated kinda in the same style that "schoolhouse rock" was animated with, at least the "I'm just a bill, sitting here on capitol hill" song. Dunno about the rest of the series, never saw it.
In this book they were telling the story about Louis Pasteur and his rabies vaccine, they mentioned pasteurization, but didn't go into how it worked. The book portrayed the vaccine in a ridiculously oversized syringe, and the vaccine inside was soldiers. Probably French legionaries, but I called them Blue Nutcrackers. That book made me understand at a kid level how vaccines work, and made me comfortable with getting them when I was 6. I wish I could remember what it was called, it really should be required reading.
Edit: Found it! It is called "The Value of Believing In Yourself, The story of Louis Pasteur.
I've seen claims that it has more nutrients in it that are destroyed by pasteurization. There are also probiotics that would be destroyed by it. However, you can get these things elsewhere with less risk of contamination.
They buy it because they are easily spooked by long words such as 'Pasteurization' and probably fell asleep during the class that talks about all of the diseases that the Pasteurization' process is supposed to prevent.
It makes delicious cheese. Pasturisation kills bacteria and denatures enzymes that are helpful in making good cheese. After proper aging, it's safe to eat. Parmigiano Reggiano is made with unpasturised milk.