User blog comment:Xilinoc/Ch. 658 - Fatal Matters Are Cold/@comment-5303512-20160115035404/@comment-1210805-20160115055656

They were probably forbidden from doing so, just like their are often restrictions placed on captains that prevent them using their full power. Gaining Hollow powers is considered illegal in the Soul Society, so the Visored who joined the Gotei 13 would probably be forbidden from using their Hollow powers.