Oil tankers are basically "weapons of mass environment destruction" (slight hyperbole, sorry ;). When you shoot at them, or their captains have the valves opened, their oil will devastate a sizable chunk of sea and coastline.
So you really need to tread lightly around enemy oil tankers.
> Oil tankers are basically "weapons of mass environment destruction"
Which is why you sink them empty. Ukraine has been doing this for months now.