You don't have to follow Elon's Twitter.

However you do have to be in work channels, and this group of people sent the unsolicited letter in those channels.

And now we're all having to talk about the letter.

Musk's behavior and actions directly impact things like hiring, employee retention and more

You can argue you don't have to follow Elon's twitter, but when you try to hire someone and they quote Elon's behavior as a reason why not to work for your company what do you expect?