Comments mention multiplexing and that’s not wrong but the real reason for the vast number of wires is amplifiers, or rather the lack of practical ones at the time. You had to transmit at high enough power to overcome losses and still be able to hear at the destination.

Each wire carries just one signal at a power that would easily interfere with others, they needed relatively thick wires separated from each other. You see pictures of poles with lots of cross bars carrying lots of wires in this period.

Once amplification was practical they could use the thin telephone wires bundled together in a cable, each wire carrying a much fainter signal that can be easily amplified as needed.

Amplification existed but it took the vacuum tube to get it affordable and reliable for each circuit to have its own amplification.