And we have 12 non-thumb phalanxes on each hand. Point each phalanx of one hand with your thumb (of the same hand), and you can count up to 12. With 5 fingers

And we have 12 non-thumb phalanxes on each hand. Point each phalanx of one hand with your thumb (of the same hand), and you can count up to 12. With 5 fingers on the other hand, you can count 5 dozen: 60. Base 10 may not be completely arbitrary, but is is undoubtedly lazy.