how come so few automakers VS boat makers?

cars are faster than boats, have less drag, more and usually shorter roads, and boating became leisure
car makers like chrysler, bmw, nissan and more made i.o. boat engines, some made boats, most boats however open
few boat designers (sports mine) designed a car, michael kasten one, martijnvE a vw and see this marchi exercise below

 

Cars vs boats?

"Mass" produced boats (not ships or Ribs) are luxury items mostly, boat building collapses every 6 years or so due to economic flux or occasional brilliance of pols to tax it away. Hardly an environment for long term capital investments. However, when global warming floods the worlds coast and 75% of people are living withing 15 miles or so, boats may become a necessity and a bureaucracy will pop up to constrain every "approved" boat to be able to brake in 25 feet, hold its lane etc.

Come on now its candy apples and oranges...

 

Is there a way to get the number of active builders from the uscg or other source?
It would be curious to know the number of independent builders now compared with 10, 20, 30, 40 years ago.