##Why is feature not enabled on Ask Ubuntu?
It's not enabled on any sites other than Stack Overflow, we're not missing out on much. It's likely only enabled on SO as that is the 'main' site. It's not a very important feature anyways..
##What does the link actually refer to?
That link just took you to the Reputation Leagues.
You can access it by going to this page, or clicking the weekly / monthly / quarterly reputation leagues link at the bottom of the Users page's Reputation tab.
Click the link at the bottom:
... it takes you to this page:
