Thanks for bringing us back down to earth. I note with interest that bcspace fled once you mentioned smelting, like a vampire from a cross.
It's very simple. You need high temperatures to smelt hard metals (note that ancient Americans did limited smelting with softer metals like copper at lower temperatures), and to do that you need the technology (in this case, a bellows). Conveniently, the Book of Mormon tells us that Nephi knew how to use a bellows to heat ore and extract hard metal:
9 And I said: Lord, whither shall I go that I may find ore to molten, that I may make tools to construct the ship after the manner which thou hast shown unto me?
10 And it came to pass that the Lord told me whither I should go to find ore, that I might make tools.
11 And it came to pass that I, Nephi, did make a bellows wherewith to blow the fire, of the skins of beasts; and after I had made a bellows, that I might have wherewith to blow the fire, I did smite two stones together that I might make fire. ...
16 And it came to pass that I did make tools of the ore which I did molten out of the rock. (1 Nephi 17:9-11, 16)
Nephi also makes swords out of smelted hard metals:
14 And I, Nephi, did take the sword of Laban, and after the manner of it did make many swords, lest by any means the people who were now called Lamanites should come upon us and destroy us; for I knew their hatred towards me and my children and those who were called my people.
15 And I did teach my people to build buildings, and to work in all manner of wood, and of iron, and of copper, and of brass, and of steel, and of gold, and of silver, and of precious ores, which were in great abundance. (2 Nephi 5:14)
The Jaredites had similar technology, according to the Book of Mormon:
9 Wherefore, he came to the hill Ephraim, and he did molten out of the hill, and made swords out of steel for those whom he had drawn away with him; and after he had armed them with swords he returned to the city Nehor, and gave battle unto his brother Corihor, by which means he obtained the kingdom and restored it unto his father Kib. (Ether 7:9
23 And they did work in all manner of ore, and they did make gold, and silver, and iron, and brass, and all manner of metals; and they did dig it out of the earth; wherefore, they did cast up mighty heaps of earth to get ore, of gold, and of silver, and of iron, and of copper. And they did work all manner of fine work. (Ether 10:23)
There is no archaeological evidence of Mesoamericans using smelted hard metals either for tools or for weapons.
But this is just the "absence of evidence." The other half of the equation is that everywhere that high-temperature technology has been introduced, it has a ripple effect on other industries. For example, pottery that is fired at high heats is of much better quality and very different characteristics than is low-temperature pottery.
So, even if every steel sword and tool had rusted away, we would find pottery characteristic of high heat. What we find in Mesoamerica is pottery created rather crudely by putting the wet pots in a pit, covering them with brush, and setting the brush on fire. Brush is added to the fire until the pottery has hardened. This is positive evidence that high-heat technology was not known in Mesoamerica, and the archaeological evidence of low-heat metal work confirms that the technology was unknown.