chrome wasn't as expensive back when it was common. I get the impression that it's not all that expensive in some countries even now. OTOH, a lot of bicycle industry chrome isn't very good.

You see a lot of chrome lugs now that are actually polished stainless. Not sure when that came about.

I always thought they fully chromed bikes, but I recently saw a Schwinn Paramount that obviously had been chromed in many steps. IIrc, the head tube lugs were chromed separately. Which still seems weird to me. I can see chroming the head tube then the seat lug then the dropouts. Even that's a lot of work when you can just put it in the tank and zap it.