Motor vehicle applications are a sealed unit. Meaning your gas that’s in your car/truck doesn’t have a chance to breathe. Gas tanks in boats are designed to breathe which means they are constantly adding and subtracting air from the tank. Incoming air means more chance of water molecules being added to the fuel. Ethanol is hygroscopic, meaning that it absorbs water from everything. Whether that’s from the incoming air or from the condensation of the tank, who knows. After sitting for awhile, you can get phase separation in your fuel. The ethanol is heavier so it sits at the bottom of your tank. Fire up your boat after sitting for a couple months and it might be sucking up ethanol instead of fuel, which is really bad for anything rubber that that shizen touches. If you’re constantly adding fuel, it’s not a huge factor as it doesn’t have the chance to separate. Some people think that the idea is all a bunch of horse turds but I dunno…..science and all. ¯\_(ツ)_/¯