“I am trying to understand what happened yesterday.”
He’s old. He’s very old at this point. The Church is very large and facing very great problems with Islam in the ME and elsewhere along with fights in the secular realm.
I think he realized the demands of the Easter Vigil were beyond his strength at this point.
IMO the next few years will be telling, i.e. will his health rapidly decline (retired due to medical condition), or will his health hold out (retired due to Vatican politics)?