While I have not been following the news, Chelsea do not have a recognized left back as far as I know with Cole gone, and a make shift right back playing left back all of last season.
If it is true that Chelsea didn't go in for him because of their other targets, than I am surprised. They plan to spend another season with no recognized left back, and no real cover in case of injuries, I'm just surprised at the short-sightedness of Mourinho.
However, if no other Clubs were in for him, then I guess the deal makes more sense to me.