The New York Times Bestseller list covers a population much larger than that. Yet:
"""To make the list, it is estimated that novels sell from 1,000 to 10,000 copies per week, depending on competition. Median sales fluctuate between 4,000 and 8,000 in fiction, and 2,000–6,000 in nonfiction. The majority of New York Times bestselling books sell from 10,000 to 100,000 copies in their first year.""" - https://en.wikipedia.org/wiki/The_New_York_Times_Best_Seller...
Anyway my argument was sorta the opposite: the book did manifestly not sell well enough that it became how most people got converted to Nazism, and if more people had read the book they might have realized that Hitler was doing exactly what he wrote in his book and stopped him at an earlier point.