It's not hard to find series where people get to redo their lives and ultimately change their undesirable destiny to become a great person or to leave a better world in their wake. Boku Dake Inai Machi, Saike Mata Shite mo, and the more popular Re;Zero are some good examples of this, and they all revolve around a common theme of changing one's or others' selves to create a better path to the future.
However, Umareru Kachi no Nakatta Jibun ga Anna no Tame ni Dekiru Ikutsuka no Koto takes a much more cynical approach to the genre. Rather than showing how people can change throughout getting a second chance, the series instead goes to portray the contrary perspective. How some people can change for the worse when they get another chance.
Our protagonist, Kazuya, is simply not a good person. He is no Okabe or Satoru, being incredibly selfish. And though the cliched "traumatic past" trope that many shut-in protagonists have also appears in this series, rather than being stopped and marred by fear of said past traumas, Kazuya vents out his undesirable past with frustration and anger. So when he acquires such a great opportunity to mold the future to his will, of course he abuses it for his own gain, and mercilessly steps on the people who he feels wronged him. While Kazuya himself is scum, he is an oddly easy character to relate and sympathize with, since his frustrations and anger are feelings that many people understand, whether they be carnal, physical frustrations or the feeling of not wanting to be the odd one out of his circle of friends.
Overall, I'd say the appeal of this series is something very akin to that of Deathnote. Everyone knows full well that the protagonist is an evil that must be stopped at all costs. However, you want to see how far he can go and what lines the character is willing to cross in his journey. This series is something very much worth reading if you can stomach the protagonist.