The WowProgress Pet Battle ranking system received an update. Duplicates are no longer counted towards your pet score. This significantly changed the top ranked players (overall), and many went from over 14k pet score to 10k.
While I'm still not a fan of a "pet score", I think this is the right step towards a more accurate and fair ranking system.
In any case, collect for your own reasons. If trying to reach top 20 or whatever is what you enjoy doing, go for it! If not, then pay no mind to the list. To each their own, and love your collection! Companions are awesome and should be celebrated as such. :)
PS: Thanks to Runestones on Twitter for the headsup!