We all have links to the Romo de Vivar and the Ruiz de Esparza?

When I read, some time ago, that virtually all families with roots in our area of interest are descendants of "Capitanes" Diego Romo de Vivar and Lope Ruis de Esparza, I thought probably that was not my case because at that time I was under the impresion that most of my father's ancestry was from Jerez and Guadalupe (Zacatecas) and my mother's mostly from Guanajuato and as far as I was aware then no Romo nor Ruiz Esparza have come out in my research. Well, I was dead wrong! obviously my research was very weak then, but as years passed and my research skill developed I came to the conclusion that on my father's family with the excepción of the Cabral main line that comes from my father's father and great grand father, on many of my father's mother's side I was overwhelmed when I discovered so many lines that joined those two families, all of them in Rincón de Romos which looks like a cradle. I tend to think that my case is by no means exceptional but mostly very common (am I right?). For instance, on the Ruiz de Esparza y Navarro family, I discovered I am direct descendant of Lorenzo, Martín, María, Salvador and Jacinto Ruiz de Esparza y Navarro, and to Jacinto I have a couple of lines that merge with him. On the Romo de Vivar family things are quite similar, multiple lines end there in Diego Romo de Vivar. Clearly, most of both names come together multiple times in my family. It is so because my ancestors ("sosa" numbers)18, 19, 21, 23 and also 33 have this multiple lines. When more carefully looking at those two families in the family search trees I see why it is said we all are part of that families at some point: they are prolific. Surely not everybody have discovered the links or maybe have non. But even so, since we all have many other lines in our are, clearly we all are "primos".