Because boats are cars too
There are issues inherent with hydrogen as a fuel for cars. It is incredibly expensive and energy intensive to create, it is difficult to pressurize and transport, and the infrastructure for hydrogen as fuel is far less developed than battery electric charging. A few automotive manufacturers, chiefly Honda and Toyota, have hung their zero emissions program hat on the hydrogen peg, but it’s still a very small sliver of the automotive market. It’s pretty much only viable in a small area of Southern California near the fueling stations. As a car fuel, hydrogen straight up sucks.
Toyota and the Energy Observer are proving that hydrogen might be best served as a fuel for traversing the high seas, however. Toyota has adapted what it has learned from the Mirai hydrogen experiment to the Energy Observer, a former racing catamaran which now travels the world preaching the gospel of maritime ZEVs.