It looks like conductivity is also desired, to some degree, to help the metal surfaces dissipate lightning.
That's basically a walk in the park compared to anything that needs to deal with unearthly temperatures and harsh chemicals at the same time. Furthermore, air (and airborne water) isn't very abrasive which helps a lot even if you do go through it at hundreds of miles per hour.
You can more or less think most modern paint as a plastic coating. High speed air with the occasional water droplet or Canadaian goose, easy. Abrasives, hydrocarbons, high temperatures, not so easy.
But in the modern age, if you need a metal mesh around a carbon fiber fuselage then not painting the airplane is probably not an option. Sad.
It wasn't quite that simple. I believe the 'bare metal' finish actually had a layer of protective varnish painted on, to protect the metal from oxidation (anyone who has handled bare aluminum can tell you that it develops a layer of oxide very quickly). In addition to that, the panels had to be specially chosen and very carefully handled, as small blemishes were very obvious.
https://www.boeing.com/commercial/aeromagazine/aero_05/texto...
> The decision to paint or polish the metal surfaces of airplanes is based on marketing, economic, and environmental considerations. Although the net operating cost of polished airplanes is slightly more than that of painted airplanes, no compelling reason generally exists to choose one type of livery over the other.