Like the GP said: in offices the floor is often a big open space where light from windows can extend a long way. But once you start dividing up that big space into smaller residential units with walls, that light gets blocked.

I don't think bedrooms really need windows and in some ways they're preferable with the light & noise reductions.

Even if that's solved the bigger problem is earthquake code. These older buildings aren't up to modern code and significant renovations would require structure changes.