Ben what a fantastic question. I assume you are asking about a guitar rather than an electric guitar. I think the answer is somehow linked to the object that the guitar strings are attached to and something called resonance.
What is resonance? It seems to be linked to a structure, box/container which will receive a vibration and amplify (make greater) that vibration. To do this the box/container has to be constructed in a partculiar way so that it is capable of receiving, amplifying and sending out (broadcasting) the new bigger signal.
Consider an empty yoghurt pot. Stretch an elastic band across it, twitch the elastic band, did you hear anything? No. There is therefore no resonance between the vibration of the elastic band and the yoghurt pot. Replace the yogurt pot with an open tin can, a cardboard tissue box, a plastic/china cup and any other object that you can get your hands on -with permission. Do any of them amplify the twitching of the elastic band.
Your guitar is a fantastic box. It resonates with the sound that is produced by you twitching the strings and amplifies the sound of that delicate sensitive twitch.
I will look again at this answer in the next two days.