I think this is due more to internal church policy rather than anything else - at least within the rc heirarchy.In that case the churches have virtually no political power. The most they can do is influence voters to favor candidates who favor one point of view or another. They can't even name a particular candidate from the pulpit.
Personally, I think they should be able to name candidates that they favor just as most major newspapers endorse candidates that they favor. As it is most churches I have been in have no official position and the work of influencing the congregation takes place one person to another - very grassroots.
Personally, I can't see any reason for a priest not to endorse a certain candidate - in his capacity as a private citizen. This can only be a problem IF he coerses others to his position using the military.