Wouldn’t companies with a strong international presence (e.g. Apple) contribute to that? It seems like increased globalization could explain that high ratio rather than “overvaluation.”
Exports contribute to GDP but sales between foreign subsidiaries do not. So a Toyota made in Toyota-owned Kentucky factory contributes to the US GDP. This is in contrast to GNP; that US-made Toyota would count towards Japan's GNP.
The metric as designed is more flawed, because not all companies are public.