ShiroKuro I think a big part of Roussea/Kassia is they identified a general preference for the Topdown perspective. That's our perspective as a default so I'd bet that's why most piano videos before them were done via sideview. Since that's the perspective we can't see.
Rousseau realizes, wait, most people actually want to see the topdown perspective, which most pianists take for granted. And he also identified the 'right level' of realism. In reality the head moves a lot, they realized the audience also wants the stability ie from a fixed overhead camera.
Some decent channels go too far with this idea, when they use the headcam Gopro. The audience doesn't want full, literal immersion, as a headcam will add in some unsettling half-baked VR tech/ floaty Oculus feel to the video and make it queasy.