The primary problem with asbestos is breathing the asbestos dust which causes scarring of the lungs. Step 1 of asbestos mitigation is to wet it so it doesn't fill the air with asbestos dust.
Sinking the ship in the ocean prevents the asbestos from crumbling into dust.
Breathing may be the primary problem, indeed. Still, I would argue that one needs to examine issues related to fish ingestion of asbestos. The issue gives pretty google, e.g. [1[
Sinking the ship in the ocean prevents the asbestos from crumbling into dust.
Ref: https://www.fs.usda.gov/eng/toolbox/haz/haz07b.htm