Occam's Razor argues that Sam simply wanted ScarJo's voice, but couldn't get it, so they came up with a legally probably technically OK but ethically murky clone.
You want Brad Pitt for your movie. He says no. You hire Benicio Del Toro because of the physical resemblence. Big deal.
Having seen "Her" and many other Scarlet Johansson movies, I didn't think for a second that GPT-4o sounded like her. On the contrary, I wondered why they had chosen the voice of a middle aged woman, and whether that was about being woke. It wasn't until social media went hysterical, I realized that the voices were sort of similar.
AIs and automated systems, real and fictional, traditionally use women more than men to voice them. Apparently there was some research among all-male bomber crews that this "stood out", the B-58 was issued with some recordings of Joan Elms (https://archive.org/details/b58alertaudio ) and this was widely copied.
(obvious media exception: HAL)