I don’t think your reason is their reason in this case. 
They probably launched it to rekindle interest in the game by playing the nostalgic card (oh, has it turned out to be a pun? ), which also doesn’t surpise me, considering the direction the game design has gone in throughout the years, but I rememeber reading something (probably this [1]) how the interest dropped quickly among the players, and so did it for the developers eventually.
With that said, I still stand by my earlier interptretation that ‘greed is good’ for them (sorry for self-repetition):
(Assumes a crazy goblin voice, think Dr Boom’s level of craziness and Gallywix’s level of greed combined) So yeah, cheapskates, enough of this nonsense, you should buy more packs! Buy, buy, buy! Did I mention buying more?
[1] https://www.pcgamer.com/blizzard-is-killing-hearthstone-classic-and-replacing-it-with-a-new-mode-called-twist/