Why do I feel this a drag? well, but the drag isn't dragging :-D Anyway, first of all their debut was delayed for almost 2 years because of YG scandals. It affected their debut and they lost a lot of fans.
Isn't 1M physical album sales great for a 5 month old rookie? They are the second fastest to sell 1M albums. If we're going to talk about why their album sales don't grow every comeback, it's because pre-release order was only 1-2 weeks only. And why do you keep comparing them in 2 year bgs? They are not even a year old group. Don't worry about Treasure they are doing good.