Because despite the bones of this scenario being a fairly simple railroad (PCs talk to NPC, go collect objects 1, 2, 3; have social encounter), the adventure takes place on another plane with fantastical creatures and requires the author to devote some time flushing those out. As a result, a lot of the "in between stuff" is left undefined.
Unlike another scenario which might tell you the names of 6 merchants the players can speak to for information, this scenario does no such thing. It just says "they can make this check and it takes this long to learn X." Well that doesn't mean that the players don't encounter 6 merchants, it just means that you get to define them. And that is freedom. Especially given the backdrop of Axis.
Axis got a recent write up in War for the Crown, as did psychopomp culture, both of which are at play in this scenario. When you go to GM this scenario, do yourself a favor and read up on those things, as well as Hao Jin herself. If you don't have access to the books, check out the Pathfinder wiki -- its not as detailed but contains the same major points. Having a strong understanding of Axis, Pharasma (river of souls), and Hao Jin, goes a long way to making this adventure stand out.
I mentioned the simplistic structure earlier, and I want to be clear that it isn't a detriment in this scenario. Yes, in almost any other adventure, the structure would be a knock against it in my book. However, given the complexity of the setting, the motivations, and the story behind the scenario, having a simple layout for the adventure is a welcome blessing. Otherwise this scenario would almost be too much. Also, the simpler the layout the more prep time you have to read up on all that juicy lore.
And man, is it good. The story the author presents here is solid. Hao Jin's motivation, the various places her memory USB drives have gone, what results those have had, the tie in with 322. But the real moment it shines is in the judges. Each judge that presides over her trial has a specific problem with what she did--make the tapestry.
Judge A is an immortal being that watches over civilizations and preserves history so it can be passed down to younger generations. Hao Jin literally abducted thousands of people from their culture and trapped them in a demi plane. Whoops.
Judge B is the herald of exactness, more or less, who is upset with how Hao Jin made her demi plane. She broke lots of laws on Axis, and Judge B knows them all. Things aren't looking great.
Judge C is a psychopomp, tasked with preserving the passage of souls to Pharasma so they may be judged and pass on the the afterlife. Any mucking about with that process is a big cosmic no-no. Hao Jin may have syphoned off residual soul stuff to make her demiplane function. So basically, she's screwed on three fronts.
But over the course of the game, the PCs can learn of Hao Jin's motivations, her process, and the details of how she did what she did and actually formulate solid counter arguments for each judge. And if they do so, they can help sway them to find her innocent of her crimes. That's freaking cool. Name another scenario where you decide the fate of an immortal mythic tiered sorcerer before a tribunal of eternal beings on another plane. Go ahead, I'll wait.