Presumably, the cardinals knew a bit about Bergogglio's history and attitudes, seeing as he was runner up in the last conclave. I have no doubts that some voted against him because the feared exactly the sort of tradition-breaking he has engaged in.
But I suspect that others knew the church needed some 'shaking up' and figured Bergogglio was the one to do it."Better him than me." Most will never admit their motives, and we can only speculate.