Google is currently defending itself in the US Supreme Court over a lawsuit that alleges they assisted the terrorist group ISIS in recruiting members after it was found the YouTube algorithm promoted ISIS recruiting videos to young men who later committed a terrorist attack.
So to answer your question using Google’s argument: they have so many videos that an advanced search feature is required to make the site usable. Their search feature only suggests things that are popular. It’s not their fault ISIS recruitment (or other violent content) videos are popular.
The counter argument is: Google is curating content by displaying things people didn’t search out themselves. This is direct promotion by Google itself and therefor it should be treated as if they are the publisher of that content. Anyone publishing violent content should be held liable for it.