It's because people aren't posting.
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Looking beyond that admittedly brilliant and deeply insightful remark

, the main reason why the forum is quiet is because it primarily consists of older (I mean in physical age) members who are busy doing other things. This is not new; it has been true for a long time. An Adventures in Odyssey-based community that consists only of adults is going to be either very serious or very dead.
The deeper question of why the community consists primarily of adults has a more complex answer.
The first thing to take into account is that the ToO isn't well-known. You have to go out of your way to look for an online community, probably on Google but maybe on the AIOWiki, before you find it. That takes a lot of work when someone could just join a Facebook group. That said, although the forum could probably be advertised better, I've come to recognize that this isn't the underlying reason, but more of a symptom of the real reason.
To get to the real reason, we have to consider the kind of people that this community was aimed towards. Because the focus is ostensibly Adventures in Odyssey, and also roleplaying Town aspects, that means you should primarily expect preteen/teenage conservative Christians who are AIO fans. I don't think it'd be a big leap to say that this was what the site's original audience tended to be like, or that most of the site's members over the past 18 years have more or less have fit into this group, at least when they signed up.
But the way conservative Christian families handle Internet usage is different nowadays. A few years ago, it wasn't so uncommon to let kids explore the Web freely or semi-freely. That has changed as the Web and the world have gotten darker. These days, parents are more aware of the risks, and prefer sites that have content that has been screened or filtered in advance by people they trust; a random internet message board doesn't qualify for this. Besides, the ToO's actual membership has shifted from its original base to be significantly older and more left-leaning, so that if anyone who fit in the original target group
did show up, there would be a culture shock when they realized that a fair percentage of the semi-active members not only disagree with most of their beliefs, but are actually opposed to Focus on the Family.
It has been my suspicion for some time that if you want a thriving Adventures in Odyssey message board these days, it needs two things:
1) Official or semi-official recognition, so that people who visit the main Odyssey website are likely to find it.
2) A guarantee that all content will be safe and in line with the worldview of Focus on the Family and Adventures in Odyssey (and their many fans and supporters).
You have to have 2) to get 1). I've floated the idea before that the ToO could be transformed to fit this mold, but nobody has ever seemed interested in making these sacrifices, because it would involve dismantling most of the current experience and history of the site. But now, even if people were willing to go along with this for the sake of the site's activity levels, the opportunity has passed.
Some time ago, the official Odyssey and Club websites were redesigned. I'm not presently a member of the Club, so I can't give a detailed analysis of how it works or what it looks like (
@snubs or
@Bren would have a better idea), but my sources suggest that it now includes at least semi-organized discussion sections. As with the comment sections before the redesign, the board is fully moderated, so parents feel that this is a safe place for their youth to go to.
That fits my first and second criteria perfectly. Their activity is booming.
I try to be an optimist when I look at the future of things I've been involved with, but the statistical reality is that the ToO (and also the Soda Shop) are probably not going to be especially 'happening' places again. We might continue to get a few members here and there, particularly older teens, college students, or nostalgic adults who have some background with Odyssey, and we might see some peaks or spikes in activity sometimes (like during the B Team's term time last year, or when the Rydell Revelations came out and everyone commented on and criticized them), but if you want to see consistent activity and energy on an AIO fan site, you have to go where the kids are. That means that the thing to do is to put down your money for a Club subscription and accept that your posts are going to be pre-screened. This is the state of the AIO online community, and it is unlikely to change, for the foreseeable future.