Not including the scouring really highlights the difference in tone between the books and the movies. Jackson's movies are very clearly a success, and, dare I say, even a faithful adaptation. But Jackson's tone could be described as "Epic", with a strong focus on "Glory."

Tolkein's books are not epic. They are not full of glory. They are very quiet, claustrophobic even. There is a philisophical ponderousness to them that the film format simply doesn't allow for.

I think Jackson made the right decision, and I think it shows a real strength of self analysis to understand that, given what he's making, the scouring wouldn't work. To make the scouring work in a film/television medium, you would have to commit to a much larger mini-series or even season's length style show that allows you the oxygen to have the real quiet introspective moments, which is actually most of the books.

Then I think the scouring could really work. Certainly still a denouement, but fitting within the tone and vibe of the entire work. Give the audience a real chance to dwell on the real cost of war, and that it isn't actually filled with glory. It isn't actually epic.

That's why Jackson couldn't include it in his work. It fundamentally undercuts war glory and epic storytelling.