Fitstly, because they like ALL
Sketchup::Entity subclasses, they are actually C++ objects that are merely exposed to Ruby. (So the normal Ruby constructor methods do not create valid objects on the C-side.)
g = Sketchup::Group::new
Secondly, because like all
Sketchup::Drawingelement subclasses, they need to be created within an entities collection context, and simply creating a “floating” reference using the Ruby
::new constructor will not do this.
… ie, the unowned group reference is not part of any model at this point, so you cannot even add entities too IT.