Audible sound has wavelengths on the order of meters or centimeters, while visible light has a wavelength on the order of half a micrometer. In this world of breadbox-sized objects, $$ \dfrac{\lambda}{a} $$ is large for sound, and sound diffracts around walls with doorways. But $$ \dfrac{\lambda}{a} $$ is a tiny fraction for visible light passing ordinary-sized objects or apertures, so light changes its direction by only very small angles when it diffracts.
Another way of phrasing the answer: We can see by a small angle around a small obstacle or around the edge of a small opening. The side fringes and the Arago spot in the center of Figure 38.3 show this diffraction. We cannot always hear around corners. Out-of-doors, away from reflecting surfaces, have someone a few meters distant face away from you and whisper. The high-frequency, short-wavelength, information-carrying components of the sound do not diffract around his head enough for you to understand his words. Suppose an opera singer loses the tempo and cannot immediately get it from the orchestra conductor. Then the prompter may make rhythmic kissing noises with her lips and teeth. Try it-you will sound like a birdwatcher trying to lure out a curious bird. This sound is clear on the stage but does not diffract around the prompter's box enough for the audience to hear it.