Sure, the set can be tweaked, although it would need to be more than tweaked to fit into any theatre on Broadway. But that isn't the real issue - more fundamentally is the fact that for Into the Woods, unlike Hair, part of the main reason many are enjoying the production is for the sole reason that it's outdoors.
Hair was a phenomenal production made only more magical by being at the Delacorte. When it transferred, it was still an excellent revival, though it had certainly lost a bit of the magic. Into the Woods, in its current state, is a production that is made worthwhile, in my view, only because it's outdoors. I thoroughly enjoyed seeing the show because it's a beautiful show and because it's outdoors. There were certainly some other highlights, but the production, by and large, is nothing special or "transfer worthy." Therefore, there need to be some fundamental changes including casting, (partially due to lack of availability of stars and partially due to miscasting) choreography because the current state of "choreography" would never work on a Broadway stage, directing, and certainly they need to decide exactly how they're approaching all these rewrites and revisions. The child narrator, lyric changes to accommodate it, and all the other book changes need to certainly be fleshed out if not entirely revisited and redone.
That makes the production more than an easy transfer and explains why it's a bit more complicated than just downsizing the set.
Scratch and claw for every day you're worth!
Make them drag you screaming from life, keep dreaming
You'll live forever here on earth.