The remaining Protestant groups in the U.S. (Baptist, Methodist, Presbyterian, etc.) can't agree on anything (oftentimes within their own denomination!) except agreeing on the Catholic church is wrong. The largest of these Protestant groups (Baptists) dominate American culture only in the deep south.
As a result, during at least the last 100 years, Catholicism has dominated America's religious culture more than any other religious group. For example, Fr. Coughlin, Bishop Fulton, Mother Angelica, etc. had an enormous influence on the American psyche that simply wouldn't have been possible in a strongly protestant nation. (When protestant leaders have mass influence in the U.S., they tend to be types that reach across ALL denominations of Christians, like Billy Graham) To see how much Catholicism dominates, look no further than our current Supreme Court and Congress. Furthermore, when you look across the U.S. from coast to coast, you will discover the Catholic church is the largest Christian group in something like 40 out of 50 states now. Even looking back at the numbers in 1990, Catholicism was clearly dominant in most parts of the U.S.:
Add to the fact that the vast majority of the founding fathers were Episcopalian (who, as mentioned before, teaches a form of Christianity almost identical to Catholicism), and the culture of America's Christians leans much stronger towards Catholicism than say, Greece, where 98% of the population is Eastern Orthodox Christians, or most of Europe for that matter.
Bottom line is this: a Hispanic in say, Georgia, who switches from Catholic to say, Methodist, will probably find himself more in sync with the local religious traditions. Not so for a Hispanic who becomes a Protesant in New York, Illinois, California, New Jersey, Colorado, Florida, Wisconsin, Mass., Ohio, or anywhere else in the vast streches of middle America. For example here in the Chicago area, 60-70% of the population is Catholic. Catholicism is in the news and affects the culture far more prominently than protestantism here.