There's a difference between going diamond with sales from Starbucks and everyone talking about you with multiple songs from your album breaking records while your two albums sell like hot cakes. then four years later you sell a million digital downloads and album sells 3.4 million in a week.

A lot of reasons have already been stated in this thread but another thing thats often overlooked which imo is essential to her status is she's the quintissential avatar of relatability in music and pop culture. There's a reason she was called the Anti-Gaga, she brought relatability as not only a feature of an artist but a brand.