I'm going to guess that there are laws that make that pretty undesirable. For example: There were (and maybe still are) gambling ships on the Ohio river and on Lake Michigan - all of which docked in Indiana. Unfortunately, such gambling was illegal in Indiana. The ships had to leave dock and go out a little on the water. Suddenly, the gambling was legal.

There are probably dozens of these laws that encourage leaving the dock, especially if you are going into international waters instead of simply between states.