To use a hoary bearded example, John Saul "would like to read" international thrillers, but found out he writes best horror-suspense. I "would like to read" hard sci-fi, but hard science burnssss, so that's the one thing I won't be writing.
I think the breakthrough novel/story is frequently the one where the writer finally manages to honestly harness what really, really interests him, angers him, outrages him, soothes him, and so on. Then the manuscript acquires authentic animating energy--a divine spark of actual emotions and opinions--and the book (the mechanics of structure and style being already more or less there, we assume)--crosses over into breakthrough territory. Or real, deep fascination to the point of empathy, of some concept or event or person.
Examples:
King works as teacher, appalled at what monsters kids and parents are, writes Carrie
Koontz finally manages to work through bad childhood. Writes Whispers
Harris--fascinations turned into creativity--Silence of the Lambs
Bloch--fascinations turned into creativity--Psycho
Martin--feels the times need an apologia of Enlightenment Humanism--shows alternative without rose filter--Game of Thrones
Blatty--fascinated with Catholic stuff. Writes Exorcist
Benchley--fascinated with sharks. Writes Jaws
Herbert--fascinated with ecology of beach, interest expands. Writes Dune
Dashiel Hammett, Raymond Chandler, Jim Thompson, Ross Macdonal, John D Macdonald--want to describe existential and social realism, with some disguised preaching thrown in. Hide it inside crime plots
Graham Greene, John le Carre--want to describe existential and social realism, with some disguised preaching thrown in. Hide it inside spy adventure plots
