A company move like this has likely gone through plenty of discussion with internal stakeholders. I wouldn't expect big company moves like this to be measured on externally visible incentives and costs. Just as I wouldn't expect any big customer of AWS to pay the externally visible price tag.
But we aren't privy to such things, and what remains of messaging is communication to people like us. Musk decided that putting a spotlight on trans youth would be the content of such messaging.
Of course another possibility is that just like Twitter, Musk ignores high level advice and does whatever he wants.
If you talk to anyone who has worked for Musk, they will tell you that he most likely woke up, saw the news, and decided to move HQ without talking to anyone.
The employees, including the ones who would have to plan all the logistics, probably found out from his tweet.
But we aren't privy to such things, and what remains of messaging is communication to people like us. Musk decided that putting a spotlight on trans youth would be the content of such messaging.
Of course another possibility is that just like Twitter, Musk ignores high level advice and does whatever he wants.