The simple fact is that the dungeon crawl adventures are easier to write, develop, and edit.
Which is, of course, exactly why they're far less useful. Dungeon crawls are fairly simple to write - draw up a map, place a few monsters, sprinkle a few traps. Sure, the crawls in Dungeon are usually more imaginative, the monsters have templates and classes, there's a good rationale for everything being where it is, and so on, but in the end, all too often this great imagination ends up leading to the phrase "...immediately attacks whoever enters the room."
Personally, I subscribed to Dungeon hoping to see more of the things that are difficult to do - villains with complex plans and motives, mysteries with clues that make them solvable, and so on. Things that I can't write myself, or don't have time to write on a weekly or monthly basis.To summarise, I agree with Yamo. And one particular point I've been wanting to make myself is "one adventure every issue." The current format has one adventure each for low, medium and high-level characters. How about each issue having at least one adventure every issue where 75% of the encounters aren't straightforward combat encounters?
Oh, and not to sound all negative, two good examples recently were Keith Baker's Steel Shadows in #115, which spent half its pages on a murder mystery, and The Death of Lashimire, which was combat focused but completely open-ended in regards to who the PCs decide to kill or ally with.