Largely because of it. The Catholic Church has been very supportive of socialist schemes, including unions that are given huge power by government. And of course, Catholics who marry early, don't use contraceptives (or abortion), and have lots of children tend to be heavy users of the socialist schemes, having rendered themselves unable to support their families without government/taxpayer handouts. I don't think you'll find a lot of "believing Catholics" voting against the various universal health care proposals. "Free health insurance from the government for my 7 kids? Awesome, of course I'll vote for the candidate promising that!"
That's funny, all the large Catholic families I know are well off. They are not down collecting WIC or food stamps. Most of them are very successful and donate with generousity. It is the CINO’s that use birth control and do not follow the teachings of the church which are polluting and destroying the Church from within.