From an industrial designer's perspective (I'm not an industrial designer), a physical camera cover adds moving parts that can break, get stuck or wear out. It also makes the laptop's lid thicker. And it adds some friction to video calls as people would just forget to open the camera cover.
Lenovo has a plastic bezel around the screen which makes it easy for them to add this feature [1]. I am not an Industrial Engineer but it would seem much more difficult to do this with glass and not impact the structural integrity of the screen.
Having just had my screen be ruined by a micro-fracture I would rather just trust the green indicator dot than be without my laptop for a week.
