Mark - so much we don't know - and will never know. He had other close students, so he didn't need Hisa, per se. I would speculate that part of it was spiting Ueshiba, and part, quite simply, was a money and prestige issue.
As for him being "surly or mean during that period," - nah, now you are reaching. He was ALWAYS surly and mean.
Sorry, didn't mean that Takeda turned to Hisa in that regard. Meant that Takeda turned to Hisa because of Ueshiba not responding, so Takeda used Hisa to get back at Ueshiba by teaching Hisa and issuing the Menkyo.