It's probably a coping mechanism for what has historically been a very deadly profession. There was in fact a culture of "miner honor" similar to how bushido applied to samurai, but it may not have been Japan-wide but restricted to the Takeda homeland of Kai where many of their iron miners came from jizamurai (peasant samurai) stock and served as military messenger in battle. It's noticeably unique because only the iron miners seemed to have had this culture while the gold miners of Kurokawa didn't.