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.

Ref: https://www.fs.usda.gov/eng/toolbox/haz/haz07b.htm