Why is Peercoin tracking below Namecoin price?

I've seen this question come up a lot since Bitcoin begun rising.

These two altcoins have historically followed each other very closely in terms of price until recently. As Bitcoin rises and altcoin prices have fallen, we have seen Peercoin (PPC) drop below Namecoin (NMC) significantly.

I believe the explanation for this is quite simple: there are more Peercoins in the market than Namecoins, therefore there are more potential sellers.

According to coinmarketcap.com/ the current PPC supply sits at around 21 million. The same site states the current available amount of Namecoins is around 9 million.