This whole “Catholic vote” is a myth. You have those who go to Mass on a regular basis and those who are cafeteria CINOS, then you have Irish/Italian ethnic Catholics whose ancestors went through Ellis Island or earlier and the Latino Catholics who sneaked across the border. These groups besides maybe going to the same overall church have nothing in common.
You have a point. If it were not so, there would be more Catholics on the top of tickets. The GOP has never nominated a Catholic for President and the Democrat's selections have been a stretch.
The GOP is becoming more and more 'pro-choice', since Giuliani was early leading the pack. Even the SC nominations had Harriet Myers in the middle. As abortion becomes more and more a missing subject at Sunday Mass [also shacking up], the younger infrequent attendees are not attuned to pro-life as the elders.
Other issues [economy, war] have the voter's attendance because of their urgent mention in the media while voting pro-life has to be more than a 4 year cicada never mentioned in interim elections.