First, because the review system is unreliable - it's prone to acting defensively in the interests of the host (Google) and making the fastest defensible decision, regardless of accuracy.

Second, because the review system is slow. Even 24-hour turnaround is slow in a setting where display rankings risk exponential falloff if they don't get traction quickly. A brief delay on a Facebook post or Youtube video can be a death sentence in terms of engagement.

I'm not sure this system will have problems; "input from" doesn't mean "giving control to". But I certainly wouldn't want to rely on the review system as a reason to trust that nothing legitimate will be restricted.