65%-90% of humans are lactose intolerant[0], and lactaid pills aren't always effective.
https://ghr.nlm.nih.gov/condition/lactose-intolerance#statis...
https://ghr.nlm.nih.gov/condition/lactose-intolerance#statis...
Europe varies greatly, with by far the highest level of tolerance in Northern Europe (I'm Norwegian, and I didn't even know about lactose intolerance until I was in the 20's - it just wasn't something that became a subject until we were exposed to more immigrants as while it existed in Norway before that it was <5%), with lactose intolerance increasing to well above 20% in many other European countris.
In any case the advice to down vast quantities as milk isn't universally applicable anywhere.
The full quote:
"Approximately 65 percent of the human population has a reduced ability to digest lactose after infancy. Lactose intolerance in adulthood is most prevalent in people of East Asian descent, affecting more than 90 percent of adults in some of these communities. Lactose intolerance is also very common in people of West African, Arab, Jewish, Greek, and Italian descent."