Probably too late to invest in the sets and time to film the scouring if it wasn't done originally. I think they have already packed up and abandoned the Shire set, so probably the "preparation" motivation!
Ginsus ready!
I wasn't thinking that he would decide to include the scouring, but I was thinking (hoping) that he might see the kinds of character things people wanted to see that he might want to try to incorporate in other parts of the movie.
But you're probably right....
::: sigh :::