I wonder if it’s more because of tools than anything. Moving from sculpting spaces in the engine with brushes and connecting portals manually, to artists making models and importing them. There’s just so much creativity and expressiveness that got lost when the production switched to a line.
(It could also be something like why we don’t see splitscreen anymore, like "it doesn’t play nice with deferred rendering)
(Or just that as visuals became less abstract people started making less abstract rulesets and spatial areas, that everything needs An Explanation couched in scifi rather than just being)