Have they? I can't think of any science fiction that takes place within the singularity. It would be like a perfect protagonist; without flaws there can be no story, but in the singularity every character would be both perfect and inconceivably alien. The Zones of Thought series (Vinge) hardly strays from the Slow zone, and never into the Transcend except by reference. Accelerando (Stross) follows humans into exile rather than continue the narrative into the Matrioshka sphere. The Eschaton series (Stross) limits itself to the effects of the Singularity on non-Singularity civilizations.
On the other hand, plenty of science fiction narrates the acceleration towards a Singularity: Fast Times at Fairmont High (Vinge), Dennou Coil (anime). Or describe the aftermath of the Singularity on those left behind: Marooned in Realtime (Vinge). Or describe a society which averted the Singularity: Dune (Herbert).
True. No writer can imagine what's beyond the singularity, as no astronomer can look into a black hole. They can only explore "around" it, outside the "events horizon".
This is by definition of singularity: if it was possible to predict what's next, then that would be just a (meaningful) moment in the human history but not the singularity.
On the other hand, plenty of science fiction narrates the acceleration towards a Singularity: Fast Times at Fairmont High (Vinge), Dennou Coil (anime). Or describe the aftermath of the Singularity on those left behind: Marooned in Realtime (Vinge). Or describe a society which averted the Singularity: Dune (Herbert).