Because it is from Mina Ojuela.  As prolific as this mine has been, and as common as galena has been elsewhere, galena specimens from Mina Ojuela are nearly unheard of.  I would not have believed that this one was from Ojuela either, except that it came from a reputable dealer of Mexican minerals who actually travels directly to the mines, this was one of just a few pieces he obtained.  

As an indicator of how rare these are, there are only 3 examples shown on Mindat, and this one probably has them all beaten.  There is a contact near the top, but quite frankly, who cares? It's an Ojuela galena.