No, actually that's false, the sub graph did not show a sharp increases with expansion launches until ~MoP, even there, the spike was relatively tame.
The increase was relatively consistent over a period of time and its decline as well, but those huge spikes weren't a thing until WoD, the subs even flatlined during Cata launch.
No, you just need to learn to differentiate, when people return to a game because of nostalgia, that's one thing.
However, when you downplay the continued success of a product by citing nostalgia, you are wrong, your previous posts did not make this distinction.
And nostalgia in this context implies that people feel solely attracted towards a game because of previous experiences, not because there is anything good about the game itself outside of those personal memories.
That's the crux, do not talk about "dim view" when you did not articulate this very simple distinction, saying something continues to be popular because of nostalgia is essentially saying "It's actually not good, people only like because of past experiences".
And frankly, i wouldn't be even surprised to learn that a lot of people are being lured to buy a new WoW expansion solely based on memories of how much fun they used have in WoW, meaning that nostalgia would also be a driving force behind Retail expansions nowadays.