It was the caliber of women he wanted.
He was the nerdy kid in class who wanted the sultry blonde cheerleader.
He felt he was attractive enough and didn't understand until he realized that being part Asian and short and not as rich as his wealthy Californian counterparts made him undesirable to blonde rich socialites.
And that made him lose his shyt.
In his world people are either inferior or superior. Blonde whites were superior because of looks, wealth and status. Blacks were inferior because not white and at the bottom status of society. Asians were inferior because not white, not viewed as attractive as white and thought they were too nerdy and socially inept which reflected on him badly, which is why he killed his Asian roommates.
Dude was just a sociopath. There's no easy way to understand him. He felt entitled to everything. People always say why couldnt some girl just give him him puss, but that wouldn't cure why he felt entitled to kill his Asian roommates. He was just loony and an a$$hole. Literally did not have the brain to see past his own entitlement