Combat tends to be the most important thing to a reasonably large chunk of players because that's what Toady basically added first.
Except for magical stuff, mounts, and sieges, combat more-or-less has a working framework, and only needs relatively minor tweaks.
Meanwhile, go look at that devpage list, and look at what Toady is trying to do with cities. Towns before this were a few random 5x5 buildings. Now they are pictures of urban sprawl. And he's only laid down the groundwork, he's going to put in much more detail on this.
Look at how little you can do in Adventure Mode right now, and look at the overwhelming number of things that are listed in that devlog.
Now, players don't come to DF for Adventure Mode, they come for the Fortress Mode, and maybe dabble in Adventure Mode. When Toady adds all that, however, there's going to be a whole new demographic of players that are going to be interested in playing DF, and they aren't going to necessarily be the same types of people who play for the same reasons you are playing.
Besides that, Toady likes to add things in broad, sweeping arcs, and doesn't care too much for tweaking and optimizing the things he's already built in general, which is a rather unfortunate fact, as it means that almost all the "easy fixes" remain broken until Toady feels like scrapping everything. (And that's partially why I think we need to make a "Giant list of easy things to fix in the raws" thread, since only giant things get his notice.)
So while there is obvious reason for Toady to fix the things that are broken and annoy the most players that he already has, there is also reason for Toady to focus upon expanding his game so that more types of players can come into the DF experience to begin with.