I suspect it's because the upper lobes get less ventilated (the volume of their alveoli change less during respiration, and they receive less new air with each breath) compared to the lower lobes, and this causes air to stagnate there more in comparison. Since centriacinar emphysema is usually smoking related, I assume it's because smoke remains in the upper lobes more. I feel like this doesn't really make sense, could be because it's incorrect or it just needs a change of wording.
Also, an extra question if it's okay, why is panacinar emphysema more predominant in the lower lobes? Is it because the lower lobes get better perfusion?