I think its the same thing in most families who have been here for a few generations regardless of Jewish or Christian.
If the proportion of Catholics is growing I would bet its because of immigration... legal and illegal. (note that is just a feel thing... I did not look it up. but my wife works in an NICU in San Diego... and it is frequently filled with cross border babies and surrogate babies. Hearing what she does at work... premies are frequently the result of fertility docs or lack of pre natal health care.
And given what a huge sample that is, it must be true.