Ian Hill has said what decided it. The Judas Priest bassist, who announced his retirement in a long statement on 9 October, told the Metal Pilgrim channel that the moment came on stage in Brussels, when a tendon in his arm gave way. He just felt a snap, he says.
That is the injury that kept him off a stage for the first time in fifty six years, in London in September, with Davey Rimmer covering for the night. At the time it read as a setback. It turns out to have been the end.
The statement itself blamed what he called the evil arthritis along with other injuries, and in the interview, reported by Sonic Perspectives and Chaoszine, he puts the two together: the arthritis had been coming for a while, the tendon settled the question. Blabbermouth headlines his answer as having had no choice.
He is the only man who played on every Judas Priest album, and the only one who was in the band on the first day and on the last night he walked off. Rimmer, who stood in for him in September, takes the job for good.