My (albeit limited) understanding is that if SBF's lawyers can convince the jury that he was simply very incompetent that would be better (still a crime, but a less severe one) than if he intentionally defrauded customers. Similar to the difference between murder and manslaughter.

I don't think he's actually trying to bolster his defense though, I think he's largely an idiot and used to getting away with almost anything with few/no consequences.