Why are you surprised?
He told us he was going to resign if his health or abilities failed, when he was elected, and again just a couple years ago:
‘‘If a pope clearly realizes that he is no longer physically, psychologically and spiritually capable of handling the duties of his office, then he has a right, and under some circumstances, also an obligation to resign,’’ Pope Benedict XVI, Light of the World, 2010
He, better than most, knows the effect on the church and the Roman curia by the long, lingering illness of a bishop of Rome.
He is 85, and his pontificate has been nearly 8 years – almost exactly the length of the average pontificate over the last 2000 years.
He is a better theologian than any pope we have had in centuries, and knows well that, like all bishops, he can resign. And like all bishops, you do the same thing with a retired pope that you do with a retired bishop – it is not such a problem.
He knows the history of the papacy, that includes some obvious cases of papal resignation (St. Pontian, Benedict IX, Gregory VI, Clement V, Gregory XII), and several others who have been removed. Nearly 10% of all popes did not serve until death, if I remember correctly.
He is also an unquestionable champion of Catholic identity, culture and orthodoxy, so no one can claim that only a “liberal” or “reformer” pope would do this, as Paul VI had contemplated doing during his pontificate.
And above all he is a man of integrity and courage, who has done what is right in the face of pressure to simply conform to unrealistic expectations. He is not resigning because of disgrace or failure, he is retiring because it is the right thing to do for the Church, and for himself.
I think I have never been so proud of a pope in a lifetime of loving the Church.