According to the US National Library of Medicine, approximately 65% of the adult human population is lactose intolerant, and in east Asia that number goes up to 70-100%.
But I’ve eaten a whole lot of ice cream and cheese and such in Japan and there seems to be no shortage of ice cream parlors in Tokyo and all sorts of cheese and milk-based confections there.
So, I am forced to conclude that I either do not understand lactose intolerance or that a lot of Japanese folks are masochists.