Because he will better do their bidding like his father did, or else.
Guardian of the Pope.
[Personal]
"For the Pope’s recent and very high-security visit to the U.S., Dr. Domenico Giani, the Inspector General of the Vatican police and security, led the team. He is also Pope Francis’s personal bodyguard. He is usually seen off the front fender of the Pope Mobile during transits."
https://foxtrotalpha.jalopnik.com/the-pope-has-a-small-but-deadly-army-of-elite-warriors-1733268646