Why can dozens of FT8 communications occur simultaneously in the space needed for one single-sideband transmission?

An FT8 signal is extremely narrow, occupying a bandwidth of only about 50 Hz. In contrast, a standard Single Sideband (SSB) voice transmission takes up about 2400 to 3000 Hz of bandwidth. Because each FT8 signal is so narrow, dozens of them can fit side-by-side in the same frequency spectrum (the "passband") that would normally be consumed by just one SSB voice conversation. Software on the receiving computer listens to an entire 2500 Hz chunk of audio and decodes all those individual FT8 signals simultaneously. While FT8 does use strict time formatting (15-second transmit/receive intervals) and packet structuring, these features do not dictate how many signals fit into a specific frequency range. Bandwidth is the sole reason so many signals can share that space.