Magnus vs Tomashevsky Blitz 2012 - why doesn't he take the knight on e7 I'm not sure if anyone is familiar with this game, I watched it a while ago and had just rewatched it now and cannot understand why Magnus didn't take the knight on e7. 

Here's the screenshot before this went down:



The moves are in this order: Green, Blue, Red. So the board looks like this:



He doesn't take the knight, why? Instead he plays Bxb2.

I'm sorry if this is obvious to more experienced players, I'm not expert by any means just trying to get someones opinion. Thanks.
Magnus doesn't take the knight because it simply results in a loss of material:

[FEN "r1bqk3/p2pNpbn/1p4p1/8/2P5/1N4P1/PP2PP2/R2QK2B b Qq - 0 1"]

1... Qxe7 2. Bxa8 Bxb2 3. Rb1 Bc3+ 4. Kf1


By taking on b2, Black threatens to take his opponent's rook, while at the same time frees the c3 square for a check, which gains a tempo. White will then either exchange rooks or move their rook away from danger, also giving Black a chance to flee with their rook.

Taking on b2 is not the best according to engines, but at least it avoids the material loss. The position is significantly better for white.