It’s not that writers of literary fiction CAN’T write good speculative fiction or even good literary fiction with speculative elements...
It’s just that they can’t do so without having read the genre!
Heng just happened to be the writer around which some of this crystallized, but she is far from either the worst offender or the loudest (looking at you, Ian McEwan).
There’s a tendency to think that an idea about how the world works (or will work, or might work, or is terrifyingly zooming towards working) and a character drama is enough to carry a novel when all the author has done was, basically, given a name and fur color to schrodinger’s cat. You cannot tell me the story of the scientist deciding whether to open the box without telling me why the cat is in the box, how it got there, who approved the funding for this research anyway.
You cannot run a book on a gedankenexperiment even one as interesting as our culture’s obsession with fitness (the act of being fit) and life. Like, the point is good, but what happened to get us from where we are now to there? Where are people with less capital? Why is the world so empty? And, let’s be real, who the hell is producing all the nutripaks?
I don’t care if it’s stated in the story, but I don’t get the sense that Heng knows the answer to that question either and there’s the rub.
But to return for a second, Heng’s novel falls into the other obvious failure of the modernist novel - the sufferings of wealthy “interesting” people who are bored with life calls into question being while the existential drive to survive of those who are underprivileged is erased. All the characters fighting for the right to live are erased by the struggles of those fighting to die (and are pointedly only accessories to their fight).
Genre mashups are tricky because they ask the writer to be equally competent in both genres, or else the gaping chasm between how well one is executed compared to the other throws off the whole book. Heng’s characters, her disallusioned and not likable in the way we want female characters to be protagonist and her driven foil are clearly from a good literary novel. But they’re not living in a fully realized world because the act of calling to the reader’s mind a world unlike the one that is or was is a skill and it’s one Heng could cultivate but she hasn’t.
And it shows.