Agree with Bone Squad on both points; I suspect it's a function of not having official team pictures yet, and that it could create an ugly tone if any move were made to appear spiteful. The veterans from last year surely had a strong relationship with Natalie, so they'll appreciate the respectful approach.
Speculation, but I bet those pictures from last year corresponded with the actual player's locker, going with the order of Seniors (alphabetical order), followed by Juniors (alphabetical order). Stands to reason that last year Seniors Cohen, Wallace would be the first two. Followed by Junior Brown. Followed by Sophomores Chou, Cox, Landrum, etc. I bet those old pictures are down within a month, replaced with pictures of the current locker residents. This year's players haven't even reported to their first class yet, so I have no problem with the fact that last year's pictures are still hanging.