For the same misguided reason they allowed 15-15 Van Clowns with Stealth back in the day, with another Stealth top-decked next turn.
I like how those bozos playing that stuff truly believed it ‘skill-testing’.
No, it’s not, because that one doesn’t have perma-stealth and reborn. 
But anyway, Rogue (well, two kinds of it: the subject and the one with a full board of 8-8 giants on turn 1 or something like it) is just one of the current parade of decks that shouldn’t exist, the others being all sorts of Warriors, about two kinds of Warlocks, annoying Sif Mages and even Zarimi Priests (‘I’m super annoying, and even if I generally stink, just like a Rogue, I can roll really high, lol!’). Well, at least those particular Shamans of the problematic sort seem to be out, and Paladins no longer ‘busted’ after the patch…
You all should be grateful to the Aggro DH (or even Hunter to some extent) for keeping a lot of this literally toxic stuff (what? The Zilliax in question is poisonous ) somewhat at bay and making room for some cool decks, like singleton Druid, for example.
PS Druid, Hunter, DH and DK are those top classes/decks I consider legitimate at the moment. A bit uncertain about Paladin, though.