I would think that it is mostly immigration, we can’t pretend to not know that literally millions of Catholics are moving to America from Mexico, almost 10% of their population lives here now.
It's almost 100% immigration, either from the North or from Latin America. The Catholic Church has no interest in converting "trailer trash." They'd lose their rep as "the thinking man's chr*stian church."
Do Catholics tithe? It’s an honest question. Because there is nothing I can think of that would be a greater racket than coming illegally into this country, taking U.S. taxpayer’s money and tithing 10% of it to the church. Of COURSE the Catholic Church would welcome all the “unfortunates” to our country. Caesar rendering unto the Pope, via us.