Why would Joseph Smith risk saying there were millions of people living in Mesoamerica?

The Book of Mormon describes high numbers of people which were thought to be unreasonable based on our previous understanding of Mesoamerica..

However recent discoveries show that areas of Mesoamerica had much higher numbers than originally thought. National Geographic reports:

Using a revolutionary technology known as LiDAR (short for “Light Detection And Ranging”), scholars digitally removed the tree canopy from aerial images of the now-unpopulated landscape, revealing the ruins of a sprawling pre-Columbian civilization that was far more complex and interconnected than most Maya specialists had supposed.
The results suggest that Central America supported an advanced civilization that was, at its peak some 1,200 years ago, more comparable to sophisticated cultures such as ancient Greece or China than to the scattered and sparsely populated city states that ground-based research had long suggested.
Most people had been comfortable with population estimates of around 5 million,” said Estrada-Belli, who directs a multi-disciplinary archaeological project at Holmul, Guatemala. “With this new data it’s no longer unreasonable to think that there were 10 to 15 million people there—including many living in low-lying, swampy areas that many of us had thought uninhabitable.
– Tom Clynes – Laser Scans Reveal Maya “Megalopolis” Below Guatemalan Jungle

Why would Joseph Smith write about populations thought at the time to be unrealistic?

See:

Tom Clynes – Laser Scans Reveal Maya “Megalopolis” Below Guatemalan Jungle

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