The audio response curves are completely different. The slope on a bass amplifier is much lower than on a guitar amplifier, as it needs to handle much lower root notes and harmonics.

Likewise a decent bass speaker/enclosure will have a lower resonance than a guitar system, but will still need to be able to handle some relatively high harmonics to give a good tone, but clearly not as high as a guitar.

Play a guitar through a bass system and it will sound flat and bass heavy, play a bass guitar through a six string system and blow the cones . .

A 4 string bass guitar is one octave lower than a standard six string, a double bass is two octaves lower, so the amplifiers for them are even more specialized.