It's not that they failed to argue causality, but they did not prove it. From II.C.b.vii (The Hindsight Defense):
> Defendants finally argue from hindsight. They claim the Grant was fair because it worked: “Tesla thrived because of the 2018 Plan.” With this argument, Defendants ask the court to infer a direct causal relationship between the Grant and Tesla’s subsequent performance. But Defendants failed to prove that Musk’s less- than-full time efforts for Tesla were solely or directly responsible for Tesla’s recent growth, or that the Grant was solely or directly responsible for Musk’s efforts. This last argument is empty rhetoric, not evidence of fair price.
> Defendants finally argue from hindsight. They claim the Grant was fair because it worked: “Tesla thrived because of the 2018 Plan.” With this argument, Defendants ask the court to infer a direct causal relationship between the Grant and Tesla’s subsequent performance. But Defendants failed to prove that Musk’s less- than-full time efforts for Tesla were solely or directly responsible for Tesla’s recent growth, or that the Grant was solely or directly responsible for Musk’s efforts. This last argument is empty rhetoric, not evidence of fair price.