My best guess is that it's the weekly limit on auto votes - the spikes are when more accounts are voting on everything, the dips when most accounts have reached their 4/5/6/7/ whatever the weekly limit is on their votes.
When the 'peak weekly limit' is over, it kicks back up again.
i guess if we get more users who set their AVs at different times, so there's more variation in when the weekly cycle starts you'd see less pronounced dips and troughs.
Posted Using LeoFinance
That might be a reason...