They didn’t. There’s the Los Lunas inscription:
https://www.asc.ohio-state.edu/mcculloch.2/arch/loslunas.html
OTOH, the lead crosses often discussed were studied decades ago by Barry Fell, who found them to be based on various Latin mottos of old European dynasties and whatnot, a modern forgery.
Over thousands of years, there were plenty of visitors and probably trade, by lots of people. Fell pointed out that the first testimony regarding Precolumbian contact was reported by Columbus, who recorded an old retired diver in the Caribbean, who when youn had found (what turned out to be) a Phoneician coin on the seabed, and turned it into a pendant which Columbus examined and drew. Columbus researched his trip by interviewing Icelanders. In the late 15th c, the abandonment of Greenland was only a couple centuries at most in the past.
The Romans were very accomplished at seagoing trade with extremely large vessels. They were present in the Canary Islands and the Azores (and were not the first visitors/residents) and apparently reached South America:
https://freerepublic.com/tag/bayofjars/index
And there’s the Cocaine Mummies:
https://freerepublic.com/tag/cocainemummies/index
These copper deposits reminded me of the story of “Saguenay” along the St. Lawrence. At the end of the following excerpt they make the link too!
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The story of the mirage-like Kingdom of Saguenay dates to the 1530s, when the French explorer Jacques Cartier made his second journey to Canada in search of gold and a northwest passage to Asia. As his expedition traveled along the St. Lawrence River in modern day Quebec, Cartier’s Iroquois guides began to whisper tales of “Saguenay,” a vast kingdom that lay to the north. According to a chief named Donnacona, the mysterious realm was rich in spices, furs and precious metals, and was populated by blond, bearded men with pale skin....
Legends about Saguenay would haunt French explorers in North America for several years, but treasure hunters never found any trace of the mythical land of plenty or its white inhabitants. Most historians now dismiss it as a myth or tall tale, but some argue the natives may have actually been referring to copper deposits in the northwest. Still others have suggested that the Indians’ Kingdom of Saguenay could have been inspired by a centuries old Norse outpost left over from Viking voyages to North America.
If the Romans were in the Canary Islands and the Azores, that could also help explain why what appear to be Roman artifacts were found on Oak Island in Nova Scotia, namely a possible spear point, and more recently, a possible Roman coin (or half of one).
Also a stone road that could possibly be Roman in origin.
https://freerepublic.com/tag/azores/index
https://portuguese-american-journal.com/carthaginian-temples-found-azores/
Carthaginian coins in the Azores:
https://en.wikipedia.org/wiki/Carthaginian_coins_of_Corvo
Vikings in the Azores (other stuff of interest)
https://en.wikipedia.org//wiki/History_of_the_Azores#Vikings