The Cash family is just famous and so more people know their history. There are many families around the world who go through much more extreme tragedies. Many of these tragedies are brought on by society in general because it caters to the people running the world. While we feel for the Cash family, we should care about everyones family also.
The death of Johnny Cash's grandniece, as a result of a Cash family curse, is absurd. Aside from Johnny Cash's initial drug addiction, which he overcame, there is no evidence of any curse. Johnny lived a long life, in the happiest of marriages, doing the thing that he loved best, music. Not to mention how successful he was at it too. If that constitutes a curse, then sign me up.
I do not believe the recent death of Johnny Cash's grandniece means the Cash family is cursed. Johnny Cash lived a long life and passed away at the age of 71. Many families face multiple deaths in short periods of time. People do not know about these tragedies if a famous last name isn't attached to them.
With the death of Johnny Cash's grandniece, rumors springing up that the family is cursed are just rumors. All families have experience death and loss. Being a famous family doesn't make you immune to death, even tragic death at a young age. There's no curse on the family. Death is a part of life, and some people end up dying sooner than others.