If you're going to judge it based upon the default artwork, then I understand why you don't like it.
This is how anyone is going to judge it. When you went to Egghead Software in 1993 and saw an awesome box for FRUA, you rushed and flipped it over and this is what you saw (sorry I can't find a better pic):
The text is very compelling and the screenshots are gorgeous.
By contrast, someone who somehow comes across the Dungeon Craft website gets this text pitch, utterly devoid of fantasy or enticement:
Dungeon Craft is an effort to develop an RPG and editor that mimics SSI's Forgotten Realms Unlimited Adventures (FRUA). A few improvements have been made over the original FRUA, 16/24/32-bit color, more levels allowed, editable items/monsters/spells, and the resulting design includes the game executable so that each design is playable without the editor. Other differences exist, but I have attempted to duplicate FRUA/Gold Box behavior as much as possible. Of course, suggested improvements have a good chance of making their way into the source code.
And the screenshots look like the ones I showed above. (In fact, the screenshots on the main page are even a little worse.)
But everything in Dungeon Craft can be customized easily...
But the question was why people aren't drawn to Dungeon Craft, and the answer is that the fantasy it's selling you is at best Pygmalion's: start with a lump of stone, and maybe you can carve it into something you can love. The fantasy FRUA sold was that at the push of a button, you are "creating the greatest fantasy game of all time--yours!"
These still look really bad to me compared to FRUA
. More playable, probably, but totally unaesthetic. No harmony of elements. They look sort of like a Geocities page?
Again, I just want to be clear: if you stripped out all the premade assets, it is insane that someone would prefer FRUA to Dungeon Craft. And since you can import assets into Dungeon Craft (provided you take a cavalier view of intellectual property rights), you could probably make it look just like FRUA. But, ultimately, only a tiny number of people would be interested enough to put in that effort at the outset, and since only a small percentage of people who started with FRUA or Dungeon Craft ever made anything worth playing, you're dealing with a tiny fraction of a tiny base. The result is not enough activity to build a community, and in turn not enough community to sustain the tiny number of people engaged in activity.
I'm not saying it's fair or just or anything like that, but that would be my explanation for the phenomenon.