Record sales have steadily decreased since 2000. Obviously due to the internet.
Now don't think this is a stan rant, but i'll use Beyonce as an example (numbers aren't accurate).

But Dangerously in love = 700k first week
Bday = 500k first week
Sasha Fierce = 300k first week

and Sasha Fierce was the most critcally acclaimed. So you can kinda see the wierd trend.

This is also why i think its a bit unfair to say "well omg ____ has sold $X Millions!" when they were big in the 90's, coz people just don't buy albums anymore when you can just download.