Board Thread:Questions and Answers/@comment-10797017-20130627100621/@comment-11051098-20131008210606

If they knew about his intellect and the possibility that he could discover what he have discovered now, they would for sure have tried to capture or kill him in Hueco Mundo. But not even Quilge Opie seemed to recognize Urahara, or even notice him.

It seems that the only things Yhwach focused on, except stealing Bankais and killing captains as a whole, was to convince Aizen to join his ranks, steal Ryûjin Jakka and kill Yamamoto, and capture Ichigo.