question about Nextdoor promoters

Hi, Neighbors. Does anyone know why there are people promoting an online network called Nextdoor?  We just received a mailer from someone on Collins urging us to join in order to share "service provider recommendations, items for sale/free...etc," the same purposes for which we have the list serve.  It seems to me that this undercuts the established list serve and thereby fragments communications in the neighborhood, not to mention complicating the efforts of folks trying to locate lost pets or possessions.  Naturally, I am wondering what is behind this effort and would appreciate knowing what you know. Thanks! Diane Stanton Avenue