Bleach, after defeating Aizen...?

Final Getsuga Tenshou is the LAST attack Ichigo used, to BE Zangetsu.

After he used that, he lost his Shinigami powers.

Hence, Zangetsu and his Hollow form does not appear anymore, because they were born from Ichigo's Shinigami abilities.

The last arc, "The Lost Substitue Shinigami" deals with Ichigo being a normal high school kid, until he meets up with the Xcuter people; people who has Fullbring powers.

>How come Zangetsu and hollow ichigo stopped showing up in the anime?

Ichigo lost his Shinigami powers. Both Zangetsu and his inner Hollow were only alive because of his Shinigami powers...which he no longer has. Ergo, they don't show up anymore.

If you're referring to the anime, Ichigo used the "Final Getsuga Tenshou" to defeat Aizen. Final being that he used ALL of his spiritual energy in his final attack to defeat him. After that, because his spiritual energy is essentially gone, Hollow Ichigo and Zangetsu are sort of nonexistent. Or at least until he figures out how to get his spiritual energy back. Hope this helps!

It's simple. because Ichigo lost his powers