BBC article which say this is all propsal and nothing been changed yet - is saying that they want all social media set to public and all data handed over. They are testing the waters and haven't yet change policy.
If you don't they can deny entry.
I assume they may be able to go to some US companies and ask - but there are non US sites out there they probably can't - so how would they know - hence some of us wonder if you have none would they assume you're lying ?
https://www.bbc.co.uk/news/articles/c1dz0g2ykpeo
As well as the collection of social media information, the new document proposes the gathering of an applicant's telephone numbers and email addresses used over the last five and 10 years respectively, and more information about their family members.
The text cites an executive order from Trump in January, titled "Protecting the United States From Foreign Terrorists and Other National Security and Public Safety Threats".
The new proposal regarding ESTA data collection for tourists invites views from the public for 60 days.
"Nothing has changed on this front for those coming to the United States," a spokesperson for CBP said in a statement.
"This is not a final rule, it is simply the first step in starting a discussion to have new policy options to keep the American people safe."
....
The Trump administration previously announced it would examine social media accounts when vetting foreign nationals who apply for student visas or H-1B visas for skilled workers.
The state department said it would conduct "online presence" reviews for applicants and their dependants, and that privacy settings on all social media profiles must be made "public" so this screening can take place.
An announcement on the website for the US Embassy and Consulate in Mexico states certain visa applicants must list all social media usernames or handles of every platform they have used in the last five years.
It warns that if any social media information is not listed, it could lead to both current and future visas being denied.
Yes they have already announced it for student and skilled workers but now the suggestion is it's for all entry. I think if I was stydying or working ie planning a long stay in a country I'd be less fussed about handing such data over for a two week vaccation of few days bussness trip most I think would just go elsewhere - which Trump seems fine with.