The reason for that is because the hull paint is poisonous to fish and plants. Copper based antifouling coatings are dangerous to people swimming in the water also. Scraping and/or sandblasting the waste from the boat may disperse the toxins into the air and groundwater. Not to mention the "ppe" personal protection equipment required in removing the product. Plus you need a certified disposal location for the waste. Dumping the waste on the ground or into the water kills the living matter near it.
