Because it's not obvious and just using that word over and over again doesn't make it true.
Did OpenAI want to use a similar voice to Scarlett Johansson's specifically because it's her, and they want to capitalize off of her fame or her personhood specifically?
Or did OpenAI want to use a voice that sounds pleasant and appealing and as it so happens Scarlett Johansson has just such a voice and used such a voice in a famous movie about a talking AI?
In other words, if Scarlett Johansson had a different voice, perhaps even an unappealing one, would they still have used it because it's something particular about her fame and character they wanted to leverage, or did they use a similar sounding voice to hers because of the technical qualities of that voice that she happens to have and which has been demonstrated by her to be effective.
There are many other potential scenarios that one can argue are relevant to this case, and ultimately my point is that this case isn't obvious unless you come to it with an opinion already made up and have failed to appreciate the numerous points of view.