I don't understand why copper isn't used more or is considered unlikely.
I understand the Bible writers & Israelite peoples/ancient peoples generally thought of the ore as copper ore & smelted it for copper & all alloys were "copper" alloys in their minds. So translators capturing the essence of their thought may prefer copper over bronze.
I also get the argument a lot of copper was really alloys & mostly were bronze alloys technically. So modern science calls it bronze age but culturally in ancients mind they were more likely thinking the term copper for all of it. Hope that makes sense.
Jewish Hebrew dictionaries and Jewish translations of the Bible always translate this word as "copper." Why would Christian translations and dictionaries commonly translate nehhoshet as brass or bronze while Jewish dictionaries and translations use "copper?"
I think modern culture we have specific uses for the different metals due to more scientific knowledge so we are dogmatic & very specific between copper bronze & brass... because we make fittings and wires and we're acutely aware of the difference.
The original writers were Jewish descendants so I don't see why we don't predominantly go with copper like them. some older & newer articles highlighting copper & ancient mines usually use the term copper. So I prefer it in translation description of Bible objects:
A 1975 "Insight on the News" Watchtower article mentions:
Ancient Mines Found
• Down in the Negev desert, near the town of Eilat on the Gulf of ‘Aqaba, a British-backed archaeological team has located what they call the ‘oldest underground copper mines ever found.’ Described as ‘enormous and sophisticated,’ the mines are believed to date from about 1400 B.C.E. They had air shafts allowing miners to work several hundred feet below the surface. According to the “Sunday Times” of London, analysis of slag samples, made by a Chessington, Surrey, laboratory, showed that the “smelting method then used in Israel was every bit as efficient as present-day techniques in separating copper from ore.” It says the discovery calls for rewriting “the entire pre-history of metal technology.”
Such discoveries may surprise archaeologists, but the Bible shows that, even before the global flood of Noah’s day, men were making tools of copper and iron.— Gen. 4:22.
A 2013 Watchtower magazine article entitled "‘Out of the Mountains You Will Mine Copper’" highlighting archeological updates mentions:
Archaeologists have discovered in Israel and Jordan a number of ancient mining and smelting sites, such as Feinan, Timna, and Khirbat en-Nahas.
The landscape in Feinan and in Timna is dotted with shallow pits, where miners extracted copper over a period of at least 2,000 years. Even today, a visitor can find green-speckled fragments of copper-bearing stones scattered about. The ancient miners laboriously chiseled the rock surface with stone tools to extract copper from visible veins. When those sources were exhausted, they dug deeper with metal tools, enlarging caves and carving out deep shafts and tunnels. In the Bible book of Job, we find a description of such mining operations. (Job 28:2-11) This was hard physical labor; in fact, from the third century to the fifth century C.E., Roman authorities sentenced hardened criminals and other prisoners to work in the Feinan copper mines.
Immense heaps of slag are found at Khirbat en-Nahas (meaning “Ruins of Copper”), suggesting that industrial-scale copper smelting was done there. Scholars believe that ores were brought there from nearby mines, such as Feinan and Timna. To separate the copper from the ore, blowpipes and foot bellows were used to raise the temperature of the charcoal fires to about 2,200 degrees Fahrenheit (1,200°C) for eight to ten hours. It usually took 11 pounds (5 kg) of ore to produce about 2 pounds (1 kg) of copper ingots, which could then be cast into various objects.
My study notes on tin I had an excerpt from Insight on the Scriptures:
Tin’s greatest usefulness, however, was as a hardening agent; copper alloyed with 2 to 18 percent tin has been found in ancient specimens of bronze.
Since they could smelt copper fairly purely I believe most sacred or religious items crafted on God's instructions were mostly copper or intended to be copper since culturally they were aware of mixing things & purity & cleanliness of things plus they had smelting areas for purifying copper from ore.
Like the copper serpent figure, I believe is copper not bronze because it was instructed by God to be nehosshet; plus we see Jewish Bibles & dictionaries say the word predominantly refers to copper.
The King James was written in Old English & usually those people referred to copper as brass back in the day & may have influenced why they used brass mostly in the KJV translation & many translations will follow suit. Plus a lot of people are staunch King James supporters like a lot of people feel this translation is sacred & we can't change it. So credibility was put to a new translation for being similar to KJV Bible, even copying it's errors. So just because KJV does it doesn't mean it's the best. I think looking at Jewish explanations & thought process is more original to the translation & why I prefer the use of copper.
Another interesting article from the Jewish perspective: Ancient Hebrew Research Center—Copper.