It's the effect the news have on people - if I told you the pope died, you might say ok, whatever. People would have turned the TV on at 7pm and found out the news. If I pushed the pope's death on you 24/7 for almost 2 weeks you might be more engaged in that information, have Heathrow cancel peoples flights, football cancelling, tesco closing, you might think about the event differently.
The pope is a bigger deal than the British Monarch, at the very least based on the number of 'subjects' they rule over.
But the monarchy is more 'tweetable'. Diana, Andrew doing his thing, Margareth doing her thing, Phillip throwing jokes around. Now we have Meghan and Harry to carry on the circus.
There is much less melodrama about the Vatican. Not as cool as doing an interview with Oprah.