Why don't we use 7075 aluminum Ethernet and USB cables?
Aluminum oxide is stable, hard (as sapphire, because it IS sapphire, aka
alumina, Al2O3), and nonconductive.   Oxide grows spontaneously on contact
with air, so an aluminum electrical connection is often unreliable.  Welding
works, and some (fluoride-based) fluxes can allow soldering, but
for crimp connections, you need antioxidant pastes and/or odd mechanical
contrivances.  Reliable aluminum electrical connections are messy or bulky.

Copper is compatible with a variety of insulation-displacement connection
schemes (basically, just a hard clip that dents the copper but cuts through plastic insulation), that stay reliable for years.   The clip parts can
be made of copper alloys, so there are no dissimilar metals issues.  Copper oxide is neither hard, nor insulating (it's a semiconductor), so copper wire just makes a better connection.