I can't speak to the intentions of the designers, but I will say that choosing untreated copper is a pretty smart idea if you're making something that you'd like to last a while. Copper forms the distinctive green patina rather quickly but that layer prevents oxidization of further layers of metal. Essentially, the green patina locks out oxygen and becomes a protective layer against further degradation of the metal. Compare this to iron and steel which will just keep oxidizing until there's nothing left of the original.

This effect is well-known to historians because it has allowed copper and other latten artifacts to survive the ages with remarkably little degradation. Notable to my field, Greek arms and armor survived in the ground even while collocated iron objects decayed into rust colored stains in the strata. That's why we've known so much about the Grecian panoply for so long while the iconic Roman lorica segmentata was a mystery until H.R. Robinson figured it out in the 1970's. Lady Liberty's skin should last a very long time despite having constant exposure to sea air.

Fun aside, if you visit the Museo della Civiltà Romana just outside Rome in the 1942 World's Fair complex you will find within a mockup of lorica segmentata as it used to be (incorrectly) understood to have been assembled. There's also a complete set of plaster castings of Trajan's Column, a very cool thing to see up close.

hi! you may be interested in this previous thread

Why would they make the Statue of Liberty out of copper if they knew it would turn green?