I think it may be a cultural shift associated with dynamic virtual community. They are not invested in you, in waiting around to see if a relationship that doesn't work for them right now is going to start working later. They will assume you are static and unchanging and keep moving. As time goes on they add friends, they prune them, cultivate them, part of constantly shifting social structures evolving on timescales that may seem to some simply breathtaking. It sort of makes sense given the amount of connection the world now has that new ways of navigating and filtering through such a sea of humanity might emerge, especially at a time of such great perhaps historically unparalleled cultural dissociation between generations caused by rapid change in the world.