To be fair, many (all?) of these ships are burning https://en.wikipedia.org/wiki/Heavy_fuel_oil, which is not at all like petrol in that it requires preheating and atomisation to burn.
It still doesn't burn well unless it's in a fine mist. Even just a puddle of diesel is actually quite difficult to get burning on its own without some other material as a wick of sorts. https://youtu.be/7nL10C7FSbE Great practical demonstration of the different flammability characteristics of some common fuels.
For the tar that a container ship burns, it's not going to be very volatile. Coal also burns quite well, but unless it's powdered, good luck trying to ignite some with just a match.
I said pre-heated. No fuel burns in it's liquid form, it needs to be turned into a gas first. If you heat up diesel it'll light extremely easily as the vapor concentration is high.
