You probably want to adjust your expectations -- hard things are hard. The article talks about concrete freeways with faded white lane markings -- those are common in California, and as a human, I have a hard time seeing the lane markings.

Humans use road markings to help drive/navigate, why shouldn't a car?

The car using them is fine. Their absence alone causing failure is worrisome.

What do you think the car should do when it can't see any lane markings?

Would also be interested in knowing what you think it does right now, in the failure scenario we're discussing.

The point is that lots of roads don't have visible lane markings. If the self-driving mode doesn't work correctly with out them then it won't work on many US roads.