They're specification wise, statically separate kind of objects: A class constructor is special and requires more "internal slots" so they live in their own vec

They're specification wise, statically separate kind of objects: A class constructor is special and requires more "internal slots" so they live in their own vector, as do ArrayBuffers, TypedArrays, Arrays, DataViews, Maps, Sets, ... But objects that have different shapes do not end up in their own vectors, since the shape is a dynamic property.