I really enjoyed this article. I don't know about whether the disconnection in society is the reason the sister relationship is so prevalent on stage right now, but I do think the prevalence of phones, etc. has increased my love of theater because it's an escape from that. I do very much enjoy seeing any of these close family relationships played out on stage.
http://mobile.nytimes.com/2016/02/07/theater/sisterhood-beyond-the-script.html?_r=1&referer=https%3A%2F%2Ft.co%2FVdjOdYsjxR