It's because Slavic vowels are voiced lower in the larynx. Ever heard a Slavic language spoken with a nasal voice? Didn't think so.
What are the cultural effects of a predilection for speaking in a deeper tone?
I don't really like high-pitched music, preferring the cello to the violin and the beginning to the end of "Stairway to Heaven." But, Western audiences find it exciting and brilliant. You can play faster up higher. Can you talk faster at a higher pitch, too? Do the French speak in a nasally tone to have a higher bandwidth?