I think SJ because of his cancer started to look closer at that industry... I will not be surprised that Tim Cook because of Steve's passing started to look too in that area and the Watch is just the first small attempt by Apple to enter in that space. Tim and Steve were close friends, and Tim being too an avid cyclist, morning gym has no problem to have a few Engineers and R&D spent in that area.
Maybe that is very obvious or something but I know for a fact that SJ had some connections to some very capable people in that field.
It might have partially been his cancer. I am convinced that he was on point nonetheless.