When your entire revenue is dependent on quantity with minimal quality investment you lose control. When you lose control things go down hill fast (just see what MySpace and Geocities eventually became). And there is currently no AI that can discriminate between poetry, let alone what certain markets find offensive.
From the other end: Although I don't understand why a potential advertiser would not want to promote their product in front of any audience. These types of things are bound to happen when you depend on a single vendor serving an entire market spanning pretty much every human endeavor, you're bound to be servicing both the best and worst parts.
Ad companies and YouTube channels alike need to turn to smaller, controllable and direct revenue models. If you make a private deal with an ad company both sides get what they want. Now the revenue is just being distributed to primarily the worst portions of society and decent content which is a minority of the 400h/min streams only gets a stupidly small share.