As far as I know, the 3d graphics in the first slaves to armok was a big reason why Tarn switched to focussing on dwarf fortress as it was. I vaguely recall reading sometime that it was too much work for just the two of them and they weren't really making great progress and preferred to focus on working on the simulation and game systems without needing to worry about a graphics engine. Even the switch to sdl was done with help from the community if I remember right.