i think considering how the arrancar's releases are equivalent with a bankai level equipment change, (from a literal sword to armor, or crazy forms, or powers) that ikkaku having a spear with no powers, to fight with, considering he was getting his ass handed to him by un-espada arrancar (double digits). And this guy is a personal servant of the espada (they seem far stronger than the first arrancar fought in karakura town) That he'll be running low on luck unless he uses bankai =/
Also, ikkaku isn't THAT strong, like he's a strong and a great hand to hand fighter, but every opponent he's fought with his staff/spear has overcome it. And ichigo curshed it with his hand way back when, unranked arrancar juuuust about killed him from punches, and smashed it using his larger size, which this arrancar has too, ultimately his pride will hold him down.
"Knowing is not enough, we must apply.
Willing is not enough, we must do."
- Bruce lee