Most human transportation terminates at ground destinations. Since the most popular mode of ground transportation is car, most folks opt to drive their cars to their destinations so they can use them when they get there. However, if, for whatever reason, the person travels via a nonground route such as sea, air, or rail, driving a car becomes significantly less convenient due to the expense and hassle of renting. Thus, alternative means of transportation become more competitive (in particular, folding bicycles).
Since driving a car to a destination usually doesn't necessitate renting a car upon arrival, the option of using alternative means of transportation such as folding bicycles does not generally benefit from the same competitive advantage for car owners that it does for boat owners.