Triple Science is seen as a badge of being "clever" rather than of being keen on science.
If schools restrict triple to higher-ability children then what else would you expect? Then as dog-whistles go, three GCSEs rather than two is a quite basic, effective one.
"parents of clever kids won't let them consider double science, or art or music GCSE,"
It's a bit like that amongst many of the highers at DD's school, which might be middling but has a significant contingent from the right side of the tracks.
Clever Y9 DD likes science so obviously picked triple, would have been talked into that by school-side if she hadn't, but she also picked both Music and Art options with my approval. She's good at both, and I don't want a pure 'academic' child at this still young age. Or for that matter a pure academic adult.
There's a bunch of folk somewhere credibly arguing for STEAM, which is STEM with Arts & Design thrown in.