My unsubstantiated theory: They have a voice trained on Johansson's body of work ready to go, but didn't release it because they didn't get her permission. This explains why they were still asking her right up to the ChatGPT-4o release. Then people (including Johansson) associate this Sky voice with Johansson and Her. OpenAI realizes it looks bad, despite not being intentional, so they pull Sky for PR reasons.