Why Don't Elephants Have High Squeaky Voices?
To answer this question we need to look at the problems our species have with high frequency sound communication. At the upper ranges of the human voice, sound is attenuated 40 dB per 100 meters. You have got to stay close to your love if he, she, or it has a high squeaky voice like this.
If we had to use long distance vocalizations to find our mates, we would have long ago selected against altos and sopranos and would have favored elephantine bellows with no gender gap when it came to frequency.
An Elephant vocalization at 30 Hz has a sound intensity reduction of 1 dB per 10 km (at 20% relative humidity). At 5% relative humidity the reduction is 1 dB per km. So when the air gets real dry, your calls just don't travel so far.