Surprising that there aren't more Farmers than Smiths.

Not really, if you think about it. Family names derived from names that were added to distinguish one, e.g., John from another. You might have John the Smith to distinguish him from John the Miller, but John the Farmer to distinguish him from John the Other Farmer? That would be John the Black to distinguish him from John the Short because the one was exceptionally dark complected and the other only 4' 3".