Unpasteurized milk can transmit Brucellosis, avian influenza (H5N1), Campylobacter, Cryptosporidium, E. coli, Listeria, and Salmonella.
Picking one of these nasties at random -- campylobacter infection can result in headache, fever, abdominal pain, nausea, vomiting, and bloody diarrhea (https://www.who.int/news-room/fact-sheets/detail/campylobacter). And that's in otherwise healthy people! People with weak immune systems are prone to worse symptoms. Imagine being the ballplayer who misses the NLDS because they're in the hospital getting IV fluids as a result of an entirely preventable infection they got from drinking raw milk. I'd be pretty angry if one of my teammates was taking risks like that.