The Tarn attempted to make a graphical game (he and his brother have always had The Game™ in their minds, and have approached it various times) and it was a complete wash; Tarn didn't know enough about graphics to do that part, and considered it as a distraction. That was Slaves to Armok I - which is why DF's official title is Slaves to Armok: God of Blood Chapter II: Dwarf Fortress.

He chose to skip all the graphics entirely, use ASCII to render the simulation, and focus on the "story-telling simulation" instead.

And though he added support for tile sets and some rendering, that's mainly how it worked since. It's taken about 2+ years for this Steam release to happen, and that's with a lot of support; during those years DF has basically been "stalled" and not much new has happened in the simulation. This has to be a bit disappointing to Tarn, as that's what he enjoys most.

It had optional graphical tilesets for a decade or so, this release is more about overhauling whole GUI. Some stuff was just plain annoying like having to manually create bedrooms from furniture. Some stuff was fixed by DF-hack project, for more sensible experience.