First of all, historically, dairy products were never a part of our history. Vietnam since ancient times relies heavily on rice as the main food source with little to no husbandry except for water buffalo mostly for plowing. We don’t have great plains that are suitable for large herds of cattle.
Secondly, the temperature is high, therefore, storing these products might be nearly impossible.
Therefore, we lack the lactase (the enzyme needed to breakdown lactose in dairy products), so the experience is quite unpleasant after consuming those things.
However, nowadays, dairy products are presenting more and more often in family milk, mostly as skim milk for kids/teenagers and butter for breakfast and sometimes cooking.