Comment by kippinitreal

I believe it's not strictly more decks, but also how often they shuffle. If they add 7 decks but don't shuffle until near the bottom, it's actually advantageous as the count can get very skewed (e.g. 50 cards left and 30 facecards remaining). However, with 7 decks and reshuffling halfway through the count doesn't reach as much relevance to the next card.