Here's why the anime hasn't continued:
* Source Material: While the anime was based on a manga, it only adapted a portion of the story. Unfortunately, the manga was also abruptly discontinued in 2017 due to the death of its creator, Daisuke Sato.
* Controversial Content: The anime's graphic violence and sexual content were controversial, which may have deterred studios from continuing it.
* Commercial Performance: While *High School of the Dead* was a popular anime, it wasn't a massive commercial success. This may have contributed to the lack of funding for further seasons.
* Lack of Official Confirmation: There has been no official announcement from any studio regarding a continuation of the anime, despite rumors and fan speculation.
So, what happened? It's a combination of factors, but ultimately, the discontinuation of both the manga and the anime left a void that has yet to be filled. While there's always a chance of a revival, it's unlikely given the circumstances.