I know a lot of people use GURPS Dungeon Fantasy as the basis for a larger, broader fantasy game. Or use pieces of Dungeon Fantasy supplements to fill out such games - providing monsters, specific rules on travel and camping and dungeoneering, and so on.
Yet DF is written on the basic assumption that you're playing a hack-and-slash game with a minimized outside world and a focus on killing and looting.
Using Dungeon Fantasy as the basis for larger fantasy games with more details outside the dungeon and a generic Town is totally fine with me. It just flat-out works once you put on all of the extras you want. It's a great basis for a larger game.
But GURPS Dungeon Fantasy supplements work for the more simple game, too - monsters, loot, dungeons, and ready-to-play templates centered on dealing with those issues.
In order to work for both, I think it needs to stay simple at its core. It needs to stay hack-and-slash.
It's easier to add on to a simple and functioning base than to have a larger functioning base and pare it down to the simple.
It's quite easy to run "DF as written" or "DF, plus all this extra stuff to make it a larger game." It's a lot harder to say, "Expanded DF with the following bits cut out because we're not going there." It's less fun, too, as a GM, to sit around subtracting than it is adding to a versatile and effective base.
In other words, if you write GURPS Dungeon Fantasy as "GURPS Basis for A Highly Developed Fantasy World That Happens to Have Some Dungeons" then it's not really going to be a good basic tool for Dungeon Fantasy. You'd have to take that bigger, more expansive DF and carve it back down to DF Lite in order to play, basically, Diablo meets Wizardry: Proving Grounds of the Mad Overlord.
That's generally why I support a very focused, very simple, quite non-serious, very town-and-dungeon, beer-and-pretzels, hack-and-slash basis for GURPS Dungeon Fantasy. GURPS comes with all of the tools to make it a world-and-politics, exploration-and-combat, social interactions-and-story, serious game. It's stripping it down to just the essentials for the lighter core that DF is all about.
Short version? It's easy to expand a hack-and-slash DF with the other GURPS books. Cutting down an expanded DF into hack-and-slash would be harder. I'm happy that the DF line sticks with the approach that is useful to the most people. Hack-and-slash DF does that.