I think succession fortresses are most successful when the various contributors share a common goal, whether it be constructing a grand narrative, attempting !!SCIENCE!!, or simply surviving a particularly challenging embark. A shared thread between the diaries really makes the experience.
As others have mentioned, DF players know what to expect these days. Everything is documented to such a fine degree that a collective sense of mystery is impossible, since one of the living encyclopedias of dwarf knowledge will drop by the thread and explain to the finest detail why this or that occurred. This is inevitable for any video game, being closed systems and all that, but it's still kind of saddening to lose that noobish wonder we all experience when first learning the game.
Boatmurdered cannot be recreated for a number of reasons, but that shouldn't stop anyone from creating succession threads. Players should just be aware that it is no longer possible to just play the game and expect interesting stories to emerge. That's not to say that extraordinary events, the kind that confound even the oldest players, won't occur, it's just that the amount of effort needed to narrate those events increases as more is known about the game.
Players need to approach their diaries with the sense that 'larger things are afoot'. All those things that make novels interesting [character development, plot, mystery, humor, irony, etc] can be applied to the diary of a succession fortress, and should be. I'm not saying you need to be good at these things, but everyone should be attempting to make something out of their writing. You can only get better.
I think you can run interesting games by constricting gameplay according to artificial rules. In some ways these rules are just another form of storywriting, since the players that design such rulesets are often trying to simulate real-world systems that aren't already simulated in the game. If you constrict your fortress to only exporting a certain good, you can immediately fill in the blanks with "royal mandates" or "oddly-obsessed manager." Constrictions naturally build narrative in the writing of players. If just playing the game is no longer immediately interesting or worthy of writing, then you need to be playing according to a sort of meta-game that represents a more challenging gameworld.
To summarize, you need to put a lot in as the OP of a succession game. The more effort you put in to the scenario, the more likely it is you will get a response in kind from your players.
I haven't really noticed a fall-off in the number of games, but it's more like there aren't many that stand out as consistently solid.