Its not one thing, its a symptom of a lot of things wrong in that society.
Schools are a mess, parents work more and have less time for their kids... A failure of a health care system for many, a social safety net which fails for so many, and a host of other reasons all contribute to killings like this. Theres the drug war....
I hate when people try to simplify this into one or two reasons why, its way more complex than that, I think yes the desire to be famous at all costs is a real point, just look at the very depressing questionares done on middle schoolers in America last year, where the answers to what do you want to be when you grow up were #1 rich and #2 famous...
http://usatoday30.usatoday.com/news/...-y-cover_x.htm