Because Cole sold 2x as much first week this time around. Or close to it. There was a big jump.
Take Care did 631k first week and 2m260k overall.
Despite being more famous and bigger 2 years later,
NWTS did 658k first week (not that big of an improvement) and 1m700k overall. (Significantly less than Take Care)
The mixtape he dropped did even less. Actually Forest Hills Drive outsold IYRTITL.
The numbers were dropping because his Core Fanbase has been shrinking, and when I say core, I mean the early fans.
Views he went full pop, no exceptions and it sold the most he's sold ever. Not because he has more core fans but because he's pop now.