There's absolutely no way they can justify not giving Adele artist of the decade. 21 alone is a reason to give her the artist of the decade. The music industry has not seen anything like it in the 21st Century, and probably will never be seen again.
The only thing that will ever come close to 21 in pure sales is 25.
Yeah, I'm sure in a decade, someone will have a 21 type record with SPS, but 21 and 25 will be the last albums to sell that many pure albums. Not only has she had basically 2 diamond albums, she's also had 4 number 1's. One of which is the best selling single of the decade (or is it second), and another in hello which broke records for most sold singles in one week. 25 also broke the record for most abums sold in one week in the history of Billboard.
It's not even close between Adele and Taylor. Adele is on another level
The fact people think Taylor could actually be number 1

Not denying her success, but come on guys, take your stan glasses off.