User blog comment:Godisme/The Fire/@comment-5356593-20120902131957/@comment-893506-20120902190953

It wouldn't make much sense, in both senses. Story-wise, the Shinigami are an army of balancers that do what they can to guide the deceased to the afterlife, which includes purifying Hollows, so they can move on to the Soul Society, and make sure the balance between the Human World and the Soul Society is maintained. If the Shinigami get into conflict with an army that can threaten any of these objectives, then in order for Kubo to be able to hold interest, the opposing group needs to be able to stand up to the Shinigami, which includes the captains. Don't forget, while they did beat Aizen, the Gotei 13 struggled immensely to do so.

Character-wise, the Vandenreich Leader came into conflict with Yamamoto 1000 years ago, and he survived the encounter. While nobody knows how the Leader is even still alive, it is clear that he has been busy since that encounter, and he was taking steps to be able to counter the Shinigami. If he led the Vandenreich without taking steps to prep his soldiers, then his followers would be at a disadvantage against the Shinigami. And the Leader knows that captains are the strongest soldiers the Soul Society has to offer, and that their trump card is Bankai. The fact that he even knows who the current roster of captains are, and that Ichigo is a factor that can disrupt his plans means that he has been keeping his information on the Gotei 13 up to date. To think that he would not try to prepare for these things would mean that he would not be preparing for the goal to purge the Shinigami. They need to be prepared to purge the strongest if they want to succeed.