Network effects by definition means the product and my experience becomes better for me “because” other people use it. Uber does not have it — in fact when too many people use it, my experience potentially worsens because my wait times and pricing (thanks to surge) increases. Google’s search does become better for me the more people use it (as long as they keep scaling the backend enough that the product doesn’t break and search continues to be near-instantaneuous for me).
What Uber does have is brand and scale — both excellent things to have mostly because it takes huge dollars to replicate it. But you can replicate Uber with a 10 billion dollar check in 6 months. You can’t replicate Facebook that easily.