It's denial.
If they stop supporting Alice now they have to acknowledge, to themselves, that they supported someone who abuses their partner and children.
Better to dig your heels in and keep supporting them and close your eyes and ears in the face of evidence.
Another proportion of her 'fans' is definitely people who are still cut up about their own divorces and barely pay a scrap of attention to the details of Alice's. She just represents the wife who won't go down quietly, something they maybe regret about their own situations. She could be anyone, do anything, say anything. I bet some of them think Betty Broderick's victims had it coming. Vile, immature people.