"Specifically, deploying multiple, distributed, mobile cohorts of NATO marines ashore will support a broader effort. To gain and maintain sea control will be long, resource intensive, and entail a complex mix of complementary measures. In Europe, NATO can marshal potent amphibious tools, but will need new employment models to use them effectively."
We can deny access by sea/ocean but then we are left with the task of cleaning it up. And with the amount of international shipping (we are about to find out how painful it is not to receive things via water port), this is a risk many countries don't want to take.