I used to think this that as well, but I have since changed my views on why he was bitter.
I don't condone violence, and what he did was absolutely wrong, and people who worship him for it are retarded. Violence is never a good answer especially if you are an Incel, people already want to censor our thoughts and our existence as a loneliness support community, and violent acts make it worse.
However, you have to keep in mind the following:
1 - He lived in a place filled with party-going Stacies and Chads. Absolutely suicidefuel for a low tier male to live. He was mogged by Chads who were not only better looking, but richer as well.
View: https://www.youtube.com/watch?v=ZacVlnU_ivM
2 - He is considered physically unattractive in the eyes of women, as you can see in some dating apps/sites experiments:
3 - Despite being hapa, he was raised in a white environment, and was attracted to white women. He "had a preference" (that's normal, teehee™) for white stacies which are the hardest type of women to get, and he wasn't very attractive himself to begin with. He had high standards and was bound to live in frustration and unfulfilled desires.
What I think he should have done:
1 - He should have gotten a rhinoplasty asap.
2 - He should actually have finished gymmaxxing, not that it would make things a lot better, but it would certainly make him look like someone who puts a lot of effort.
3 - Moved away from that place, live on an area where people are closer to his looks levels.
4 - Taken the Blackpill. He was desilusional, thinking that the world owed him something while not accepting the fact that he lost the genetic lottery. He deep inside knew women were hanging out with "obnoxious guys" because they were better looking than he was, but he seemed to focus more on how unfair it was instead of acting on it and improving his looks. Yes, it is unfair that women select men based on genetics alone and not for hard working or fun personalities, but that's life and how the female nature works, he couldn't do anything about it outside of changing himself to applease women in order to get his dick wet.
5 - Lowered his standards on women considerably.