Why is wiring made of copper if silver conducts better?

Cost, by a wide margin. Silver is about seven per cent better as a conductor and many times more expensive, so copper wins on any calculation involving more than a few centimetres of wire. Copper is also abundant, ductile enough to be drawn into fine wire, and solders easily.

Aluminium is the interesting compromise. It conducts worse than copper per unit volume but far better per unit weight, which is why overhead power lines and aircraft wiring are aluminium - the pylons are holding up the cable, so weight is the constraint rather than cross-section. Aluminium house wiring was tried in North America during a copper price spike in the 1960s and 70s and caused fires, because it expands more with heat and creeps at connections until they loosen and arc.

Silver does get used where the cost does not matter. It is in high-end audio and RF connectors, in printed circuits, in satellite and military contacts, and it is standard for electrical contacts in relays because its oxide still conducts, unlike copper's. And superconductors have no resistance at all, which is what MRI magnets use - but they need cooling to a few degrees above absolute zero, which is why the grid is not made of them.