Neither Ireland nor Australia [whose many original citizens were prisoners from Ireland], had THAT many immigrants coming to them.  Today, Australia's entire population is the size of the entire population of either the State of Ohio or Pennsylvania.  When the Czech Republic was part of the Soviet Bloc of Nations---how many people were immigrating to it from Eastern European nations?  VERY FEW!

But the U.S. had immigrants from all over Europe----including Eastern Europe.  Today, there are also many people in the U.S. who are Catholics from other parts of the world and are Catholic obseving the following Rites:
Coptic, Ethiopian, Syrian, Maronite, Syro-Malankara, Armenian, Chaldea, Malabar, Belorussian, Bulgaian, Greek, Hungarian, Italo-Albanian, Melkite, Romanian, Ruthenian, Ukrainian, Krizevci, Albanian, and Russian.

That is why the adjective "Roman" or "Latin" is used so often here.