User blog comment:Xilinoc/Ch. 610 - Mausoleum of Skulls/@comment-9096222-20141223172751/@comment-5398287-20141223173847

It's, uh...it's been over half a year since that battle occurred, but there's a good chance he:


 * was too caught up in his anger at the girls attacking his men to take it off
 * didn't think he'd need it off for such small fry - remember, he only took it off against Ichigo once the latter proved he was a strong opponent, and against Nnoitra it came off on accident
 * forgot due to not being the sharpest knife in the drawer

Either that or Kubo forgot. However, it wouldn't really have made a difference because of the insane injuries he had already accumulated by that point - being struck by lightning twice and hit with the equivalent of a freight train just proved to be the blows necessary to bring him down. Moar Reiatsu wouldn't have done a damn thing if they could already hurt him at that level.