Facebook might just put it in their EULA since Facebook is user generated content. An automated filter isn't needed to forbid something from being posted on your site. Google however is not user generated pages, so they need an automated filter.
OK but won't Facebook need an algorithm to determine which posts do not comply with their EULA?
Why would they need that? As soon as someone notifies Facebook that illegal content has been posted on their site they will remove it, just like how it works with other illegal content like copyrighted books etc.