The Export STL item appears directly in the File menu rather than appearing in SketchUp’s Export Dialog; whereas the STL Import uses SketchUp’s built-in Dialog. This inconsistency is due to a lack of functionality in the Ruby API and prevents extensions that have an export feature from using SketchUp’ built-in export dialog and instead use a regular menu item.
This causes an inconsistency in the user interface for the STL Extension and any Ruby-based extension that wished to export from SketchUp.