Star Wars: Rogue One - 11 Biggest Unanswered Questions
8. Why Didn't The Rebel Spies Know About The Death Star Sooner?
The Question: Considering that the Death Star took approximately twenty years to build, is freaking gigantic, had apparently more than 2 million people on-board at the time of its destruction and the rebels seemingly had spies embedded in the Empire for a while, why didn't they find out about its construction until just before a weapons test was due to take place?
The Likely Answer: The real answer is simply because there wouldn't be a movie otherwise, and honestly, there's not ever likely to be a canonical explanation for this simply because it's so ridiculous that an object that's 160 kilometers in diameter and houses so many people could ever be hidden from anyone.
Rogue One may fix a lot of the bizarre fanboy nitpicks from A New Hope, but sadly not this one.