For instance in one game a dragon attacked my fort. NBD. Everyone got inside and I was planning to catch it in a cage trap. Then use it as a decoration.
However there was a group of Human traders at my Trade Depot. They decided to run over and fight the dragon. Now the dragon is running around breathing fire. Which started a forest fire. Which destroyed my wooden bridges and doors.
Completely unscripted fun, just a result of the game simulation.
Also the game manages to make you hate goblins and elves through your interactions with them.
In evil regions eyeballs grow out of the ground, blinking at passing dwarves. However cattle will happily graze on them.
If you "delve too greedily and too deep" you'll unleash horrors of the underworld.
I never understood the appeal of Dwarf Fortress until a good few hours into my first game I had just finished following a detailed tutorial and was starting to get a hang of the interface. I decided to start work on my first big construction project - a deep pit to keep the regularly attacking trolls away and a gargantuan drawbridge to lead over it. It's probably child's play by any non-noob player's standards, but I was so proud of it. All of the noble dwarves came to the grand opening of the drawbridge - the mayor, the sheriff, the captain of the guard and all of the highest ranking military dwarves in their bright shining armor. They all stood at the base to witness the first lowering of the grand drawbridge. It was lowered and with a mighty crash, flattened the gathered nobles and military elite...Because I had placed it facing the wrong way.
The fortress didn't last too long after that. I tried my best to clean things up, making a nice new dining hall and brewery, but the remaining dwarves took it pretty hard - one of them ended up losing his mind while drunk and slaughtered most of the rest in the great dining hall, the rest died of disease because nobody wanted to clean up the mess. I was so proud of my towering (and first!) fortress, and I lost it all because of one stupid mistake, but it's definitely the most fun I've ever had losing a game.
A lot of it had to do with creatively told stories about the events in a playthrough, particularly with some succession games - games passed along to others after a set time elapses. The first one I'm aware of is Boatmurdered:
I played NetHack for a long time and wanted something more. NetHack becomes pretty repetitious after a while. I tried various roguelikes and hit upon DF.
Also, I see Dwarf Fortress as the natural progression of programming games. As programmers, we always look to abstract away busywork. DF takes away the busywork of dungeon-building and hands it off to little applets.
Basically it became popular by word of mouth. I think the popularity of Minecraft led more people to hear about it, since Minecraft was said to be influenced by it. But as far as I know, it's always been a slow build, never went viral or became an overnight success.
I first saw it because someone made a calculator within their fortress. That interested me, but I don't know of any particular thing that made it popular with "the masses".
