Reputational risk. Some journalist gets wind of an ad on Youtube that's playing for a neo-Nazi video, it gets written up as "$COMPANY is supporting Nazis!" despite the fact that it's largely out of the control of $COMPANY, several companies collectively freak out and pull advertising money, and everyone goes hunting for where their pipelines might lead to similar pearl-clutching associations and PR disasters.

But that doesn't explain the documented unethical - if not illegal - conduct of Wells Fargo overall. Otherwise they'd be more like the Disney Co.