I think the demand for a new wave was there before the internet assumed its central prominence in fan discourse. I saw the new wave emerging out of the discussion in the Horizon Letterzine, which was circulating at a time when relatively few fans were online. The later pivotal role of the internet for facilitating discussion, and simply bringing people together to share ideas, is of course undeniable.

If any one event generated the new wave, it would I suspect be the BBC's release of the whole series on video. That brought a whole new crop of active fans into fandom. But some at least were not new to the series, only new to fandom. They had been quietly nurturing their fannishness, alone and in private, for a decade or more, and this inevitably individuated their interpretation of the series. And these interpretations subsequently proved to be at odds with what fandom had been doing over that decade, hence the impulse to break away from the established fandom tradition.

That, at least, is a potted summary of my own experience, though I doubt if it's unique.