Because sound does travel up? Is this a serious question? Assuming it is, you can prove this yourself with a simple experiment. Go stand on your roof. Now, drop something onto the ground below you, preferably something breakable, and drop it onto something it will break against like concrete (not necessary, just helpful).
Did you hear it hit the ground? Congratulations the sound traveled upward to your eardrum, and you’ve discovered sound does in fact travel upward. In fact it travels in all directions because sound is just air molecules moving around, which is why there is no sound in space (where there is no air).