They do it because of the sharp radial like bend in the fill hose going to the tank. There is nothing wrong with the hoses, but the fuel slows down at the bend (a lot) and then fuel overflows as you noted. All the advice you have been given is fine, and if any of those things are found, it will worsen the issue you are having. To make things worse, I've seen boats with an "S" in the hose where the fuel pools in the bottom of the "S" on a vertical axis and they really fill up painfully slow. A lot of us just live with it....