Because it is broken and full of explosive material.
https://maritime-executive.com/article/uk-is-latest-to-track-movement-of-cargo-ship-laden-with-ammonium-nitrate
From a German website:
https://www-tagesschau-de.translate.goog/ausland/europa/frachter-ruby-100.html?_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=de&_x_tr_pto=wapp
I think I have become paranoid about asymmetric tactics, but how would you stop this from going into a port if the crew was determined?