If you think Uber "must" do this if required by law, you don't get UX... They could almost certainly comply with any law like this by adding a tiny little "Tip

If you think Uber "must" do this if required by law, you don't get UX... They could almost certainly comply with any law like this by adding a tiny little "Tip your driver" link in your receipt, which would be seen and used by .001% of riders...