I tend to play a fort until its "stable" with all the industries working full time, then abandon and create a new one somewhere else. It's because i get bored of nothing really happening other than churning out goods. I tend to get bored sometimes and go off and do something else with games. I love dwarf fortress, but i keep doing this. The initial setup and startup of a fortress is a lot more interesting to me than when the fort is all ready to start trading, which is when my fort starts stagnating and getting boring.
I hear ya, buddy, this is exactly my problem as well. Part of me can't fathom the idea of deliberate sabotage just to move the game along.
On the other hand, recently I've got better by introducing little things and trying out new concepts, and my current fort is now 6 years in and I'm still vaguely interested (had a side diversion getting people killed in adventurer mode in a different crapsack world for awhile, but now I'm back).
Those things were:
+ Getting a multi-z-level channel going to let a waterfall into the main hall then move the wastewater along into the first cavern layer to prevent any chance of floods. That took about a year of planning and work in the current fort. Hilariously enough it was apparently really inspirational for the dwarves too; they ended up making two artifact floodgates afterwards which I installed into the system, which was nice.
+ Designing a new throne-room for my Countess
+ Building a danger-zone to mince invaders, complete with two unavoidable ballistae, three tame giant cave spiders and about 10 menacing glass spike traps. That took a couple of years.

+ Designing the run-up to the fortress to force caravans to only come from one direction and use the blasted road. Hilariously, Migrants always come from another direction, and every time they do, they have to wander through the gore splattered danger-zone.
+ Just designed a nice granite catacomb for the dead rather than having them all uncermoniously being put in coffins in what was effectively a hole in the wall.
Next Goal: Upgrade the danger-zone with archery pillboxes.
Next Goal: Steel weapons for all despite no flux
Next Goal: Create a new underground army base ready for breaking into the first cavern layer properly. Two forgotten beasts have spawned down there already, but since the only route to my fort is the single channeled hole with roaring 7/7 water falling 15 Z-Levels, they've just been content to sit around. Preparing, and taking them on ought to be !FUN! but I'm going to make sure I do it on my terms rather than sabotaging my chances. This will probably take a few years.