You do not understand the ways of Toady One. He is not a business, he's just a guy trying to make a fun game. He's invited people to come along and experience the journey with him (and help him test it out as he goes along). At the end of the day, I don't think his main goal is to sell Dwarf Fortress, its just to create the best game possible.
If Toady stopped working on the backbone of the game for a while so he could make some fancy graphics, he probably could do it. People would probably be happy with no new features for a while if it meant that they would get a nice, smooth, working interface.
However, then every time Toady added new features (which is constantly) he would have to tweak the graphics, at least a little bit. It would complicate every single new release quite a lot. This would mean longer times between releases. So the end result is that it would take Toady longer to finish his ideal game. Adding graphics at this point would move him further away from his end goal.
Of course, he could avoid this problem by hiring somebody to do graphics for him, but he doesn't seem to want anybody else messing with his code.
This is why I think DF is going in the best direction. Toady is making the best game that he sees fit, we are just happening to be receiving the best game that man could conceive I would argue. The 2D looks of ASCII or tilesets do what Toady wants them to do, make you envision the world yourself. DF isn't about completing the quests or about making it look the prettiest, it is about exploring a near-infinite possibility generator. Graphics suddenly limit what you see to what they want you to see. Procedurally generated creatures become a problem, as do sizing and the such. How big is one space? How can you fit 100 dragons in one square if you can see all 100 dragons?
From an interview" Shared projects like Boatmurdered mark the extent to which Tarn accommodates multiplayer participation. Massive multiplayer online games have been a lucrative industry trend for years, but Tarn disdains M.M.O.’s. To him, they replace the deep pleasures of imaginative game design with the novelty of community and are invariably oriented toward mass, lowest-common-denominator appeal. “Half the people I met were 12-year-olds yelling homophobic slurs,” he says.
At bottom, Dwarf Fortress mounts an argument about play. Many video games mimic the look and structure of films: there’s a story line, more or less fixed, that progresses only when you complete required tasks. This can make for gripping fun, but also the constrictive sense that you are a mouse in a tricked-out maze, chasing chunks of cheese. Tarn envisions Dwarf Fortress, by contrast, as an open-ended “story generator.” He and Zach grew up playing computer games with notebooks in hand, drawing their own renditions of the randomly generated creatures they encountered and logging their journeys in detail. Dwarf Fortress, which never unfolds the same way twice, takes that spirit of supple, fully engaged play to the extreme.
Tarn sees his work in stridently ethical terms. He calls games like Angry Birds or Bejeweled, which ensnare players in addictive loops of frustration and gratification under the pretense that skill is required to win, “abusive” — a common diagnosis among those who get hooked on the games, but a surprising one from a game designer, ostensibly charged with doing the hooking. “Many popular games tap into something in a person that is compulsive, like hoarding,” he said, “the need to make progress with points or collect things. You sit there saying yeah-yeah-yeah and then you wake up and say, What the hell was I doing? You can call that kind of game fun, but only if you call compulsive gambling fun.” He added: “I used to value the ability to turn the user into your slave. I don’t anymore.” "