Its because, Magic being as big as it is, is printed mainly in two different countries US and Japan
By stripping abilities before the destroy effect happens, it bypasses Indestructible (sorry, Avacyn) and turns off When this creature dies triggers (goodbye, Wurmcoil Engine)
Nadir Kraken and Chasm Skulker have synergies with drawing a card, something that you expect to do a lot with your commander
(Ouch!) Also, the fact that the creature slowly grows over time meant that development could be a bit more aggressive in the costing, as you won't immediately have a giant flying trampler
The fact your creatures can come in with Flash allows you to expand your board freely, with the added bonus of coming in with an additional +1/+1 counter
You can either force each opponent to pitch two cards and lose two life or put a non-dragon creature from any graveyard onto the battlefield at the cost of two life