Certain populations worldwide are much more lactose intolerant than others. Why might this be the case?

Lactose persistence, and therefore lactose tolerance, is inherited as a dominant trait. Lactose intolerance is the result of  having two identical alleles of a particular gene or genes. for the recessive lactase allele that is poorly expressed after early childhood.

You basically can get it from your parents.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.