I went through ESTA last winter and it was optional.

I think at the moment there is the soft problem of delays in results or potential rejection for unknown reasons. You also don't have to tell them who you're staying with either but a rejection can be pretty devastating so there is a strong incentive to give more than what is explicitly required. It was clear such encroachments on civil liberates were coming so I've never done anything on my social accounts that would upset the establishment, so even in my own case it has had a chilling effect.

If my memory serves me right, it was mandatory to mention the first address I went to, but social media was clearly marked as optional. I put GitHub, it worked fine.

My point is that it’s unknown if not stating it would impact the application so people would err on the side of caution and compliance.

Throwaway account, but this is very much like the "member of the Nazi party" question: of no practical value (border guards don't know the entire Nazi membership archive by heart, of course) unless they need to throw the book at you for some other perceived slight (i.e. involved in some political protest that is not an actual crime? HE LIED ON ENTRY FORM, IMMEDIATE EXPULSION!).

So if you don't plan to commit crimes or otherwise confront the authorities, you can leave that blank, or use throwaways. Just don't give your real info, because they will use it to analyse you for real.

A few years ago I ordered some items from a small online shop located in an east-of-central European country. A few days before I received the package I noticed that one of the recent searches on my linkedin account was from someone in that country's customs office. Not sure if they were bored and curious or working through their customs protocol.