Short form, semi-official response.
All the Catalyst sites went down due to a major hack. The BT forums were just one victim.
Professional web providers were brought in to manage the rebuild - we've been burning too many volunteers who've given of their time, skill, and blood, to keep the old stuff working, and it was time for a change of approach. This did slow things down while the new folk came up to speed on the 'historical curiosities' aspect.
And then we hit problems with the restore of the BT forum backup. After a number of attempts to restore the most recent backup, they made the call to fall back to an older copy, which we're now running on. Yes, less than ideal, but it's the first major data loss since 2011. For a volunteer-run forum, that could be much worse (eg. how many times did we lose the whole forums between 2000 and 2010? Five times? Six?)
Remember - CGL pay for the site & storage, but (until now) all forum work's done by volunteers - both front-of-house & back-of-house. The handful of people actually employed at CGL are not web gurus, nor do any do any tech stuff - they're too busy trying to get books out the door.
And yes, we're looking at options for better comms in the event of any future outages. Things like a splash screen from Word of Blake, at least. But concentration is currently on restoring service. And as the blessed Blake says, "Behind our efforts, let there be our efforts."
W.