Because it’s not a Catholic thing. Any more than black or hispanic protestant voting is a non-catholic thing.
If you go in with the wrong premise, you end up with wrong conclusions on which you base wrong solutions.
For crying out loud, of course it is a catholic thing.
Republicans have never been able to win the catholic vote, and will never be able to, that is why the left prays for more catholic immigration.
Even Catholics who pretend to be conservatives won’t do anything to interfere with that denomination’s vote, except to pretend that it doesn’t exist.
The republicans won 48% of the Catholic vote, and that might be as good as they ever see from those who are members of the Catholic denomination.