It is not feasible to send the data from voice directly from one end to another. The audio and voice frequency range is 0 to 15 kHz. The reasons are:
All sources of transmission have the same range of frequencies. So voices from multiple sources will interfere in the air and so on the receiving end, the signal will be distorted. Modulation allows signals from each source to be modulated separately to a different frequency. Then on demodulation, the data signal is restored.
Also, without modulation, it is not possible to share the vast amount of transmission bandwidth in air/space.
with modulation, the quality of the received signal can be controlled. Signals can be transmitted in hostile, noisy environments and properly recovered.
without modulation, the power requirements to transmit the signals will be higher.
Lower frequency waves will require larger emitters, antennas to transmit or receive the signal effectively.