I've thought the same thing. But it's not really a contradiction. There is room here for free will and human judgement, regarding the decision to resign because of incapacitation. The pope has prayed about it, and according to him, this is the decision that he feels called to.
The previous pope believed that he could witness to the value of suffering and aging, by staying in office.
Both are reasonable decisions.
I think JPII is who I had in mind with my comment. Also, he’s resigning as Pope, not as a Christian, as he points out he will continue on in prayer.
I wonder if he has an idea of who his replacement will be? Interesting times.