If a film was about knowing what happened, we would simply read the plot on Wikipedia. It's about experiencing it.
It's also about the director deciding whether it makes his story better--in his judgement, clearly this was not the case. You are, of course, free to disagree (no one should object to that) but the idea that audiences do not have to be shown a resolution to every single element that was introduced earlier is a legitimate one. I hate when films spend too much time explaining things I can easily figure out for myself as though I was not intelligent enough to do so.
In this case, I can see the appeal of the cut scene, but I think it's placement in the structure of the final moments of the film would have proved somewhat problematic (along the lines pointed out by Franklin
). But that's just my opinion.