This question is best answered after reading about what Top Earnings are see - http://poqery.com/505/what-does-top-earnings-actually-mean
On the right side of the same row where you can choose the leaderboard you are most interested in, there is a drop down with "Lifetime", "Month", "Week" and "Day". These selections only sample the data for the entire time a player has been on the site, the current calendar month, the current calendar week and yesterday's actions respectively.
So you could very easily have been active yesterday and taken the lead spot for Top Earnings - Day, but still may only be 100th place in the Month's standings.
So your placement changes depending on your activity for the different periods of time you choose to view.