Evans had a good eye for little details that made an image interesting as well as a natural ability to compose and crop out in camera all extraneous details.
When looking at many of his photos you cannot find a single aspect that does not belong or does not make the image stronger then if it was excluded.

One interesting aspect of Evans is that he knew most of the movers and shakers in New York publishing as well as people such as Edward Steichen when he started the photography department at MOMA. IIRC from one of his biographies there were some pretty derisive comments about his work in a letter to Steichen from one Ansel Adams.