It’s not that they “choose not to”, it’s that it’s simply not possible!
It’s not possible if they have the policy that anybody can upload / uploads are instant / whatever their current policy is. But if they changed their policy so that nothing could find its way online until it had been robustly checked, then such damaging content wouldn’t find its way onto YouTube.
But if they took this approach, they wouldn’t be able to continue making the same amount of money they currently do. So the consequences of damaging content getting online is basically seen as collateral damage, whilst they continue to make money.