Why can oil tankers flush oil into the ocean?

Oil tankers can flush oil into the ocean due to a process called "ballasting," where residual oil is mixed with seawater to clean the tanks. This practice, although illegal and harmful to the environment, sometimes occurs to avoid the costs of proper disposal. Regulations like the MARPOL Convention aim to prevent such discharges, but enforcement can be challenging. Additionally, some older or less scrupulous operators may prioritize profit over environmental protection.