And yes, they get to recover the copper, at the very least to make treatment easier for discarding (copper is a very bad pollutant). But not only there's a cost, this is dealt with by waste treatment companies that will at most use the copper value to recoup some of the cost of the treatment.
We've been doing something a lot like this for as long as I can remember.
Back in the 1990s if there were any big unused copper areas on your PCB you'd mask them to save on etching acid - a gallon of acid would have a lifetime measured in square inches of copper removed, and the less copper you removed, the longer your acid would last.
Meanwhile, a lot of DIY etching processes were very basic. Sure, you could get translucent acid and a transparent bath and heat it to a controlled temperature and run bubbles through it and so on. But if you were on a budget, some room temperature ferric chloride in an old ice cream container would get the job done. And getting the etch resist onto the board? You could draw it by hand with special pens, use transfers, there were special printer toner transfer papers, or you could DIY UV photoresist using printable projector transparencies and the sun as your UV source.
This was not a super-scientific, tightly controlled process.
If you had narrow traces and narrow gaps on one part of your PCB, and large areas of copper to remove on another? Well, if you left it in the acid long enough to remove that large area, could be the narrow traces get etched away too.
So masking off any large areas meant all the copper getting etched was about the same width - thus compensating for the poorly controlled etching process.
Of course, these days professional PCB manufacturing is orders of magnitude cheaper than it used to be. When you send your design to pcbway or jlcpcb they have much tighter control over the process, so you no longer have to worry about this stuff.
IMHO Ethernet is one of the of great examples of backwards compatibility in the computing world. Even the wireless standards present frames to the upper layers like they're Ethernet. It's also a counterexample to the bureaucracy of standards bodies --- the standard that actually became widely used was the one that got released first. The other example that comes to mind is OSI vs DoD(TCP/IP).
Sounds like a cautionary tale: whatever gets released first will stick. If you make a blunder, generations will have to live with it (like IPv4).
This whole thing just won't go away because many people are operating outside their area of expertise on this subject.
Painters layer paint, starting with a saturated base color. These archaeologists are simply looking at the paint that was left in the crevices.
"The paints used in the reconstructions are chemically similar to the trace pigments found on parts of the surface of the originals. However, those pigments formed the underlayer of a finished work to which they bear a very conjectural relationship. Imagine a modern historian trying to reconstruct the Mona Lisa on the basis of a few residual pigments here and there on a largely featureless canvas.
How confident could we be that the result accurately reproduces the original?
This point is not actually disputed by supporters of the reconstructions. For example, Cecilie Brøns, who leads a project on ancient polychromy at the Ny Carlsberg Glyptotek in Copenhagen, praises the reconstructions but notes that ‘reconstructions can be difficult to explain to the public – that these are not exact copies, that we can never know exactly how they looked’."