"A review of these releases also found that the rhetoric in the press releases on abortion and gay marriage is relatively mild, while the releases devoted to immigration, refugees and health care are passionate." 

Thomas Reese, does anyone care, let alone read, what bishops put in their press releases?  You use the wrong yard stick to measure bishops' political activity.  What matters is what they do at election time and what they raise money to campaign on.  In recent decades, they have told voters not to vote Democrat.  They also raise millions of $ to fight SSM.