Some think that the question is not why is the rest of the world not drinking milk, but why does the West drink so much of it. Phrasing the question this way also takes away the implication that something is awry with the diet of the rest of the world when it is not like ours (including ecologically, a la Diamond's Guns Germs and Steel. And it is not clear the relationship with cows is that symbiotic either, consider Ben and Jerry's on down, dairy products aren't necessarily benefitting the health of adults.).
But it may be worth considering that something is in our diet that we would be better off without.
(Although when asked by non-Americans why don't Americans eat more tofu? or why don't Americans exercise more and lower their fat intake? I hear the implication that something is not right with my country's diet and find it hard to disagree...)
The attached link is just one example of the many works out there on this subject, it is a World Bank view. Lactose intolerance appears to be one the least of the worries when it comes to high consumption of dairy products spreading to the rest of the world.
Incidentally, my recently-come-to-America Chinese husband is trying to force his lactose intolerant body to get used to milk, and I can only say "why?". Even though i can understand why he would like to fit in with American cultural dietary norms, along with trying to fit into the rest of society, he would be better off without our milk, ice cream, butter, cream etc. and should stick to the healthy Chinese lots of vegetables, tofu, seafood, seaweed, nattou and some meat dishes that he often cooks (ok, the seaweed and nattou part comes from years spent in Japan...).
Washed down with a glass of warm dou jiang (soy milk) or high antioxidant tea can't be beat.
I can understand why the Chinese government is trying to introduce milk in schools, because it promotes growth and strong bones, the reason why still-growing youngster mammals drink it. The Japanese government instituted a similar school lunch program after WWII; it is popular to this day. But what does it do for adults.