This doesn't really explain the problem. Fragmentation and creation of new fandoms had been going on in significant quantity for at least a decade before the supply of new trufen started drying up. I'm half a fringe fan myself, being heavily involved in Tolkien fandom for just as long, and it is that, not fanzine fandom in particular, or even pure SF fandom in general, which has first call for my time and resources. (That's why I hardly ever get to Wiscon.)

The professionalization of convention-running has certainly not been responsible for the impact on fanzine fandom, as they're quite distinct parts of the subculture with relatively small overlap. In fact, convention running seems to be one of the more healthily growing parts of the older field.

The real question is, whence this unwillingness by neos to learn the folkways, lingo and customs of the group they seek to join? That's what's new.