Elliot Rodgers was a sociopathic narcissist - his parents did try to get him help, and did try to socialize him -- but there was perhaps no stopping that black hole of a personality. He was incredibly self-absorbed and entitled, and had zero compassion, self-awareness, or empathy for others.

The last straw for him - the party that triggered him to commit the shootings later - was one where he made an ass of himself. He would notice girls talking to other guys (while ignoring Elliot himself), so he'd interject drunkenly, start acting arrogant, and insulted everyone. He also tried pushing people off a ledge (and failed) and instead got pushed off himself, resulting in a broken ankle. He also noticed someone had stolen his Gucci sunglasses, and went to the wrong house in his drunken state, trying to start fights and getting hit back.

And yet he had the gall to say, "The worst part of this whole ordeal was not getting beaten up, oh no. It was the fact that no one showed any concern." He proceeded to ramble on about how he was so alone, nobody cared, whatever. Yet not once did he take responsibility for the fact that this whole thing was self-inflicted, being aggressive and even trying to harm other people, and then crying foul when they fought back.

He was mentally ill and I don't know what would have fixed it. His core belief system seemed to revolve around the fact that he was naturally superior to others and didn't understand why people didn't fawn over him. He never showed empathy to others yet demanded it himself.

In this sense the answer again boils down to socialization - there needs to be some component present for getting along with others, learning how to talk to people, all that stuff. The pathway there may be different for different people, but I think a big part of what makes an incel an incel is this utter self-absorption that clouds their inability to see things from the perspective of others.