“Today I Found Out” is an interesting series of shorts, and I found “Why Are Today’s People So Much People than Historically?”
The average height for males in the US is 69 inches, and the country with the tallest people now is the Netherlands (just over 72 in). The narrator attributes increase in height to better nutrition and fewer diseases. Whatever the morality of the situation in the early USW (slavery), the system of large privately owned land holdings improved the quality and quantity of food production relative to population (a typical libertarian argument).
Humans are wired genetically to benefit from height up to about 72-74 inches, and above that, excess height (however attractive) can become a medical liability later (sometimes it is associated with Marfan syndrome). However, it seems that the tendency for men to grow slightly taller with time continues. On any crowded disco, there are always a few men (usually white) over 76 to even 78 inches, towering above everyone else.