He seemed pretty lukewarm about it all at first.
From the Guardian: '...we decided somebody should put their hat in the ring in order to promote that debate. And, unfortunately, it’s my hat in the ring.”
Why did it have to be his hat? “Well, Diane [Abbott] and John [McDonnell] have done it before, so it was my turn.” So he took some persuading? “Yeah. I have never held any appointed office, so in that sense it’s unusual, but if I can promote some causes and debate by doing this, then good. That’s why I’m doing it.” He offers a tiny smile. Blink and you miss it. “At my age I’m not likely to be a long-term contender, am I?” '
He wasn't too enthused about it. So I suppose I would have liked him to be a bit more inspired by the prospect of leading the Labour Party than just saying, "well Diane has had her turn, so now I suppose it's my go".