Why Bandwidth grows with how much information the signal carries. CW is just an on/off keyed carrier sent at a few dozen words per minute, so it only needs roughly 100 to 300 Hz. SSB voice needs about 2 to 3 kHz to pass speech frequencies, slow-scan TV occupies a similar voice-sized channel because it is audio tones, and FM voice spreads out to 10 to 15 kHz because of the frequency deviation plus sidebands.
Watch out SSB voice is the narrowest of the voice modes, which makes it tempting, but at about 3 kHz it is still ten or more times wider than keyed CW.
Bandwidth ladder: CW (~150 Hz) < SSB/SSTV (~3 kHz) < FM (~10-15 kHz) < fast-scan TV (MHz).
Morse is dots and dashes, the thinnest marks you can make. CW is the skinniest signal on the air.