Well, one-time posters cannot be the problem; more likely a symptom, I'd think. The question I'd ask, is why some first-time posters never return (even to read their own threads), and why some do. To return, I'd guess one would have to be somewhat serious about what they posted, and they'd have to get some kind of reassurance from the replies to their thread. We all know this, right?

The forum does change over time. They all do. All we who are presently posting can do is try to steer the tone and the subject in the direction we hope the forum moves, and hope for the best.
That's why I hardly ever post in threads about UO-8's and Varsities or, for that matter, a good many other things that don't interest me.