Why can't conductors be used in making ICs (integrated circuits) instead of semiconductors?
Semiconductor diodes can rectify current and transistors may be linear amplifiers by using a small modulation to create a large output swing  of the output voltage or  output current limited by resistance.
They may also be used as switches with limits on voltage and current output.
Conductors may be used as switches may not be used to amplify.  Relays can be magnetically moved to operate conductive contacts.
“Semi” implies that depending on bias current or voltage on input the output can act like an insulator or a conductor but with polarized constraints.