Because WiFi and sound waves really have very little in common other than they are both “waves”.
Sound is a mechanical wave, while WiFi is an electromagnetic wave. Middle school physics said that “mechanical waves need to be transmitted in a medium” and “the transmission of electromagnetic waves does not require a medium”, which is of course true, but there are some supplements in undergraduate physics. As long as there is a medium, sound waves can almost propagate, and even the more “dense” the medium, the better the propagation effect (a partial differential equation about the modulus is omitted here). For electromagnetic waves, many media can shield them. For example, a thin layer of metal can shield almost all bands of electromagnetic waves—microwave ovens, sunlight, WiFi signals, etc. (a partial differential about the skin effect is omitted here. Equation); wood, walls, human bodies, etc. can also shield electromagnetic waves in the visible light band—after all, they are opaque; even metal meshes with air leakage everywhere (that is, “Faraday cages”) can also shield electromagnetic waves quite well. For sound waves, concrete itself is a very good propagation medium, and the loss in the process of passing through the wall mainly comes from the reflection of the wall surface; for electromagnetic waves, in addition to the reflection of the wall , the absorption of electromagnetic waves by the brick wall itself, the reinforcement in the load-bearing wall The equivalent Faraday cage formed will attenuate the WiFi signal.