User blog comment:Xilinoc/Ch. 670 - The Perfect Crimson/@comment-25897574-20160415040047/@comment-3423279-20160415133942

Isshin explained while Ichigo was in Jinzen that Zanpakutou don't like to teach their wielder techniques or something like that, and you need to fight them to learn.

However that might of been specifically for Final Getsuga Tensho....