nullc parent
There are some places where a car ferry is essentially a bridge and just operate as part of the highway, e.g. there are two such instances in sacramento: https://dot.ca.gov/caltrans-near-me/district-4/d4-projects/d... The rides are about a minute long and you very much wouldn't want to change vehicles.
Another common scenario is vastly different population density on the far side of the ferry route. It seems unlikely to me that autonomous vehicle companies would want to maintain a giant seasonal fleet at such destinations.
In a lot of cases rather than seasonal it will be a surge every weekend.