XD I know that much of the why, I was more boggled over the logistics of the titular Vice-President spending four years imprisoned in the Department's of Administrative Research's office space. Did he have, like, a cot in a corner of somebody's office, or a proper living space? I am really amused to imagine him sleeping under a desk but am sure this did not happen.
Meanwhile to avoid getting too far off topic, the Aerith/Nanaki plan has always struck me as a point in favor of Hojo being as bad at science as Sephiroth claimed. I mean, he gets the credit for making Sephiroth, and he gave Cloud his enhancements, but the cell-infusion technique seems to have been standard across the Jenova Project, and Lucretia is unlikely to have *not* made scientific contributions and we know she was very good at making human bodies sync well with nonhuman energy...
;] Plus Jenova is highly contagious. I don't think transferring her genes is as hard as it would be with anything else.