Ichigo's Hollow mask used to be a core part of his identity as a character, but after his battle against Aizen and he lost his Shinigami powers, he never once used it again in the series.
So, why not? In this video, I give my speculative thoughts on the subject, looking at why I think, both in-universe and narratively, Ichigo's Hollow mask may have been removed for good.
Enjoy.