Here is the explanation that can also be found on the page:
Note: This is a living document and will continue to update these numbers nightly until the season ends.
After sampling some of smaller BGs for inactive teams and comparing it to samples from the larger BGs, I have found a what I believe to be a safe and accurate approximation for the percentage of inactive teams. When comparing the new numbers with the last year hallf of fame, it seems to be a slight increase, but not massive which is what one would expect. To see the discussion on this, feel free to check this thread.
Inactive Team Estimations:
Here is how the tables below are generated:
First, apply the estimates estimate to the total number of teams to find how many gladiators and duelists there will be.
Next, scan through the active teams until those numbers are reached and record their rank and rating.
This gives us the estimated rank and rating cutoffs for those titles.
If anyone can post a similar thread to this on the EU, KR, and TW boards I would appreciate it.