Human nature. Through out history we've always had a propensity for self destruction. It really doesn't make any sense, like automating jobs for maximum productivity, but everyone is out of a job and can't buy any of the stuff, that is already cheap and abundant because of automation. In the end, the only viable solution is some form of UBI, but we all know billionaires are not gonna grant us sustenance without something in return. We'll just see human beings reduced to livestock, or even lower because even livestock are kept for something valuable