The small overlap test is designed for situations where cars hit one-another, head on, on a narrow two lane road. So making changes only to the driver's side makes some sense here, because it's always the driver's sides that impact in this test. It's less "optimizing for the test" and more "optimizing for results", as these accidents used to be the most deadly type of accidents.

Additionally, this is a really, really difficult test to pass, which is why everyone failed it. Even the revisions didn't help too much because there's not much that can be done to an existing chassis other than add a deflection bar or something. True success here requires ground up engineering.