@atomicpoet much of the recent growth has been reported by mastodon.social (see @tchambers per-instance decomposition). If people just registering count as active, and the MAUs reported by these instances is going down, it means more accounts are going inactive than new ones are being created. This is compounded by an increase in spam accounts, that get blocked more or less quickly, abd probably instance migration (does the old account still count as existing?)