Why is 7 Bd3 in the Cambridge Springs QGD more often met with 7...Ne4 than 7...dxc4? My question relates the Cambridge Springs QGD when Black deviates from the main line by playing the well-known inaccuracy 7 Bd3.

[FEN "..."]   
1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Bg5 Nbd7 5. e3 c6 6. Nf3 Qa5 7. Bd3


I had always been taught to play 7...dxc4 8 Bxc4 Ne4 here. However, searching an up-to-date database of OTB games I see that of the 292 games to reach the position after 7 Bd3 118 players chose 7...Ne4, while only 97 chose 7...dxc4. Furthermore of the 13 players above 2200 who have got to this position as Black, 8 chose 7...Ne4, 4 chose 7...dxc4, and 1 chose 7...Bb4. 

However, I don't understand why this should be. It seems to me 7...Ne4 8 Bxe4 dxe4 9 Ne5 (the usual continuation) White is doing relatively better than they would be doing after 7...dxc4 8 Bxc4 Ne4. 

Am I missing something, or is the case that Black players are making a mistake by choosing 7...Ne4 instead of 7...dxc4?
7...dxc4 is absolutely just as good as 7...Ne4. Stockfish 10 (at depth 32) gives 7...dxc4 an evaluation of -0.31, while 7...Ne4 is 0.23. A difference of 118 games vs 96 games isn't a big deal and has very little weight in determining the objective strength of a move. So this is one of those cases where deciding which move to play is a matter of taste.

EDIT - according to online saved results, Stockfish (as of Aug 1 2019) at depth 47 gives 7...dxc4 a -0.43 evaluation. So it's definitely sound :)