What fundamental engineering philosophy defined the Lambretta's structure compared to the Vespa's design?

Answer

It leaned toward a more motorcycle-like construction with the engine largely exposed

Lambretta adopted a more motorcycle-like construction where the bodywork acted more like fairings, contrasting with the Vespa's structural monocoque body.

What fundamental engineering philosophy defined the Lambretta's structure compared to the Vespa's design?
inventionVehiclemodelscooterLambretta