Because CMOs typically don't formally write to business partners, "I'd like to confirm in writing that we'd spend lots of money with you but the ADL is bullying us"? I mean, sure, it's possible that these conversations were in written form even if unlikely, but then what's Musk supposed to do, put private emails from potential customers out in the open? And why would the ADL itself put this stuff in writing?

If he gets discovery against the ADL then he can see how widespread it is using things like internal documents too, and build the case directly with that, instead of having to go via whatever scraps other businesses will give him.