The children of powerful men tended to marry the children of other powerful men, so the lines of many of these families and other powerful families tend to mesh and twine together over the intervening years. Some of those lines continued into other powerful families. Some lines continued into less powerful but perhaps wealthy families. Along the way, someone fell afoul of some bit of misfortune or hardship and emigrated. A few dozen generations later, here we all are, so many of us descended from all or most of the Barons who left any lines to this day and age.
Incidentally, most of us likely also descended from the cow herd who tended the Baron's beef, the stable hand who shoveled what stable hands shovel, and the peasant who resented the other two for their good fortune. It's just that the last three mentioned didn't leave much in the way of records of their lives the way Barons did.
