"Boozy Grandmas"

I found an article form CNN that caught my eye.  The title was Boozy Grandmas, not exactly two words that are normally seen together.  The article was about how television shows, and even some movies, are using a grandmother who drinks to add some humor and drama to the show.  I feel a "boozy grandma" would attract people to watch a show, its so unexpected that many would find it humorous and intriguing to see and old woman in such a light.  

The article describes the hard-drinking grandmothers on television shows to be "wealthy, white and cruelly witty, with poor parenting skills."  The last description of a boozy grandma, a woman with "poor parenting skills",  is what really stuck with me.  Why would there be a correlation between bad parenting and a drinking grandmother?  I guess a better question to ask is, why do the people creating these characters believe that a grandmother who drinks is automatically a bad parent?  In addition to the boozy grandma, it is common to see an alcoholic father in television shows.  Why is it that we seldom see an alcoholic mother?