Edit to add: I wonder if Wynston ever wondered why the Empire had not managed to build something like Coruscant, if the Empire was so perfect. (They can't they can only take it and then break it in their efforts to "perfect" it.)
I'd have to guess it's a combination of population and history. The Empire is much much younger than the Republic or Nar Shaddaa even this early in SW history. It's also more remote, being based on the rim as opposed to in the core. I don't think the Empire has as many people in it (even including the slave population) as the Republic as a whole. Dromund Kaas could potentially develop that way given enough time.
Then there's the whole Sith infighting thing--their paranoia and constant destroying each other isn't conducive to extensive urban development.
Fun episode, btw. I really liked Wynston questioning the withdrawal from the Imperial perspective. There's been some examination on Republic side, but little on the other. I wish we saw more of it.
@ Ves: Interesting ending. You also have a good point in your title--there are lots of ways this story could go. I did like the way you did the last section.