My answer is this
activity is a value that get stuck on specific values till all conditions are met.
everything else is secret to avoid people focusing on optimizing for ranking up.
Wow, this I would say is well thought out, a very good idea indeed, this will make users pay more attention and focus on being their real self, rather than trying so hard to become who they aren't.
And by this, the forum will be able to know who is actually working hard, and they will be rewarded accordingly even when they were just being natural self.
The more time I spend here, the more i see this forum as an improved version of btt, just hope it becomes as big and popular as btt, or even better.