They press against the back of the door panels to keep the panels snug against the door handle bezels, otherwise over time you may end up with a gap between the panels and door handles, if the panels begin to bow in.
Some people install them backwards, with the small diameter end towards the door panels, then wonder why they work their way through the panel holes.
Vila
1933 Chevrolet
1962 Triumph TR4
1984 BMW 633 CSi