The Seismic Experiment for Interior Structure probe onboard the Insight lander is meant to measure subtle seismic events on Martian surface.
In order to reduce the noise induced by wind, a protective cover is installed on top of it.
Is it essential for this cover to have a bellows design? Why would not a standard rigid cover do the job of wind protection?
Image for reference from Spaceflight 101's InSight Instrument Overview "Wind & Thermal Shield – Image: CNES/InSight Project" (courtesy @uhoh's answer).