My guess would be it's too much of an "in your face" shot with the locomotive up close like that, but it's a tricky crop with all those telephone poles and empty trees. Try backing out a bit if you can and see what you come up with.
They're probably saying you should've gotten the shot at more of a profile to the train as opposed to a rather head on shot. That way, it eliminates quite a lot of the right hand 'dead space' by filling it with train.
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Can you put the tops of what look like transformers back on at the right/top if not the whole pole? Or even get rid of all of those poles all together. I'd cut from the top to keep your aspect ratio then if that's the case.
Also, is the paint faded that bad on 2 different models of BNSF locos? Looks like you need to juice the orange up a bit. The rest of it looks OK.
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