The time, expense, and depletion of medical resources in the US to contain the disease is insane.
Exactly! Why let these people on a plane to the US?
As someone indicated, the horse is already out of the barn by then!
So they carefully quarantine the IDed traveller - but then he has exposed a hundred people to the virus! Great! They get to leave and poison everyone else!
You are right - a ship would be great, but still preferably at the OTHER shores, not ours - how are they going to transport people to these ships?