because he had a bunch of children and spread their genetics all over england by giving them land and titles leading to your richard, duke of york types who had a bunch of sons and spread them around all over with land and titles. eventually they run out of land and titles and offspring begins breeding with the peasantry. but keep in mind this, being descended from directly from this paternal line would still be rare. they are counting all connections to the family tree. basically all our family trees are pretty connected and only removed by so many cousins if you really think about it.
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