I guess it might also come down to fighting distance. If you are at an striking and grappling range (as common in Goju Ryu and Uechi Ryu) you may be more prone to kick low.
From a further distance high kicks and jumping kicks could perhaps be better applied. Also kumite-formats may have had their influence.
Old school karate didn't promote competition matches that much, more so matches for the sake of learning.
Just thought though.
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Ives