They likely have a legal position which is defensible.
They're much more worried that they don't have a PR position which is defensible.
What's the point of winning the (legal) battle if you lose the war (of public opinion)?
Given the rest of their product is built on apathy to copyright, they're actively being sued by creators, and the general public is sympathetic to GenAI taking human jobs...
... this isn't a great moment for OpenAI to initiate a long legal battle, against a female movie actress / celebrity, in which they're arguing how her likeness isn't actually controlled by her.
Talk about optics!
(And I'd expect they quietly care much more about their continued ability to push creative output through their copyright launderer, than get into a battle over likeness)