The people who make phones can make voices sound better, but they just haven’t.
Many years ago, scientists at phone company labs studied how many of the frequencies they could take out of the human voice and still have clear comprehension.
They then deliberately cut out all the “unnecessary” tones, the highs and lows mostly, which dramatically reduced the amount of power and phone-line bandwidth needed to transmit a phone conversation.
Will sound quality improve over time?
Maybe, but despite huge strides in audio quality in recordings, radio, movies, and television, consumers have gotten used to that tin can quality on phones and apparently don’t seem to mind it.
At least not enough to complain to phone manufacturers.