Obviously, this is true, and it's something we haven't discussed too much.
However, we should also recognize that this is more than just a trope: loneliness is a theme that runs throughout the whole genre from Mary Shelley to Oryx and Crake. If we wonder what purpose this genre serves, or why we always go back to it, one answer is that we all confront loneliness, and the premise of all these stories--an Earth emptied of its human masses, through whatever series of events--is the perfect vehicle for confronting and exploring loneliness.
We can expand this further still: if this genre is more popular than ever, and loneliness is one of the chief themes explored in the genre, does this mean that we are more interested in loneliness now? Does it mean that we are, in fact, lonelier than ever before, despite all our social networks and constant contact with friends and family?