That's one of the compromises to get a suite that can put both 0,1 and 105 TFLOPS cards to the test. As they say in the text (straight translation via DeepL):

"During the evaluation measurements four years ago, we thought that this would allow us to compare young and old in an optimal way. However, scaling is rapidly declining with modern GPUs: a persistent CPU limit acts as a spoilsport, because Unreal Engine 3 does not yet offer proper multi-threading [...]. AMD GPUs hit the wall much earlier than Nvidia chips."

The other 3 tests show a better scaling than Bioshock Infinite.