Let us understand this by considering a hypothetical situation. Let us assume that India has not ratified MARPOL convention. There will be further two situations in this assumption.
- India would have its own pollution prevention rules
- India does not have any pollution prevention rules
In the first case, there would be lesser ships eligible to enter in India which would mean higher costs for cargo transportation. India would not want that.
In the second case, the coastline of the country would be at a higher risk of oil pollution. India would not want that either.
In the third case, India can implement same rules as Marpol without ratifying it. This would be an illogical thing to do because if there is nothing in a convention that a state has to object, ratifying a convention would bring better cooperation among other states that have ratified the convention.