> Boats have had a higher level of autonomy than cars for a while.

This is really a mixed bag - some categories of vessels have had more advanced navigation systems for decades, but on the the other hand a family minivan is about two decades ahead of a bowrider that goes for about same price when it comes to autonomy.

More directly addressing the article - marine autonomy is an easier problem technically, but there is a significant market problem. Aside from water taxis, there is not the same compelling economic case for autonomous small boats as there is for commuter cars.

Disclaimer: I work on ADAS systems for recreational boats.