I'm not really sure how to answer that. It is just a known fact that the subway platforms are all supposed to be level with the train floor. Platforms can sink

I'm not really sure how to answer that. It is just a known fact that the subway platforms are all supposed to be level with the train floor. Platforms can sink and otherwise decay over time. Many of the stations are quite old. Low platforms, by contrast, are nowhere near the height of the train floor.