Because the disease is endemic everywhere but Australia. It is a problem for the United States because it is also endemic in the United States, and the United States cannot escape the consequences of a new outbreak of the Black Death in the Old World or the New World.
I think you missed the point of my comment - Some reporter in Britain is asking why WE haven’t done something - since when are we responsible for solving the worlds problems?
There won’t be a new outbreak, this is pure fear mongering at it’s most offensive and disgusting.