Cause the novel only has one volume so it was either axed or left incomplete by the author. The manga is an adaptation of the novel and since there's no more material to adapt it likely was axed when the novel stopped
I checked this cause the anime started and honestly don't get it. There's dozens of these unspectacular/mid manga that are at the same level of art and storytelling but average at least 1 full point higher. I think the standards by which the people are reviewing it are hypocritical since I went...