Which part of the open letter discusses working conditions?[1] It's about how they don't want to work for a company owned by a person expressing their opinion in the public sphere because it causes embarrassment in their own social spheres being voluntarily associated with that.
The court case is now about them demanding to have their jobs reinstated to a company owned by that exact same person where absolutely nothing has changed.
I agree that workers should have freedom of speech, but the owner of the company they work for also has that same right, a right they oppose and which seems to be the root of all their problems leading to this case.
Freedom of speech was never freedom from consequences was it.
[1] https://www.theverge.com/2022/6/16/23170228/spacex-elon-musk...