Completely sidestepping whether OpenAI did a scummy or underhanded thing here: I don't find Sky's voice to be all that close to Scarlett Johansson's. Scarlet has a "hoarseness" to her voice that is completely missing from Sky. It's difficult to describe, but you can see hear it in any clip from the movie Her, but that's what she actually sounds like in most movies.

I can completely buy that they were looking for a voice actress that sounded kind of like Scarlett, but this mimic isn't perfect because it misses this "raspiness".