Yes, this question has been broached before: Cardinal as a middle name
So, that thread managed to settle the origins of the term “cardinal”, their distinctive plumage, and that the AP no longer uses the style. What it doesn’t cover is why.
Yes, someone quotes the AP stylebook as saying that it’s associated to the customs of nobility, but I really can’t buy that. “William, Duke of Norfolk” was not “William Norfolk” from birth, but “William Cardinal Keeler” was always “William Keeler”. Also: as pointed out above it’s “William Cardinal Keeler”, not “William, Cardinal Keeler”. The whole AP explanation smells strongly of a backwards guess by someone who had to come up with something to put in the guide but really didn’t know what he was talking about.
Another twist: a number of websites I’ve run across in my recent readings have actually consistently italicized the title. Thus, “William Cardinal Keeler”. Is this part of the standard?
So, within the last week I’ve learned pretty much everything about the College of Cardinals that I wasn’t taught back in Sunday school (which amounted to “above an archbishop, below the Pope”) but this irritating bit. Can the SDMB irregulars come up with an answer before they become strongly inaccessible cardinals?