Cheap labor. There's plenty out there. Google will tell them what the facts are and they'll promote/hide stories based on truthiness.
As I pointed above, it doesn't seem like Google is even marking stuff has "checked", but marking articles as being themselves "fact checks".
The perception of whether Google is good or not is all that matters. This is how media and mass psychology works. This isn't about fact-checking stories. It's about using Google's brand to deem specific stories to be real or fake.