Why A CW signal is just a carrier switched on and off, so the only thing that spreads it out is the keying itself. The faster the keying and the sharper the rise and fall of each dot, the wider the sidebands, but at normal hand-sending speeds the occupied bandwidth is only on the order of 150 Hz. That narrowness is why CW receivers can use very tight filters and dig signals out of noise that would bury a voice signal.