Why is outer space devoid of gases?
Right, first of all there are gases in space, you hear about the clouds of gases & dust in space I am sure?
Just this gas is spread out.
There is still gases in space, just not in giant mixtures the way our atmosphere is.
There is still particles & atoms of what you may call 'gas' which can still move around much like our own atmosphere's, but are very sparsely spread out, but yet this doesn't mean you can't hear sounds but you'll need an extremely sensitive microphone to hear anything like this from space.
The best example is a black hole, scientists have aimed one of these microphones before at one at the centre of a galaxy & the sound they got back from it was the lowest known sound in the universe, 57 octaves below middle C (on a Piano that is) which is a frequency more than a million billion times beneath the limits of the human ear.
Hopefully this helps.