Typically, little people have shorter legs. ^ Generally, shorter legs fit more easily under seats in the row in front than the legs of taller people with longer legs. Height, perspective, and basic grade 7 or 8 geometry matters.
By contrast, taller people have longer legs. Generally, longer legs do not fit as easily under the seats of the row in front or available allocated space by row. Result of the latter: leg jam. Hence, why some taller people try to create more available space, e.g., sitting atop blankets or pillows.
On any flight more than 2 hours, no clue how sort-of-tall people (6'-6'2") sit in non-exit row economy seats now. Or, how anyone 6'3+ fails to pay the nominal amount for a few extra inches of space. Invest the 25 Spartacus bucks!