Re a privacy issue: Here in the EU we have a thing called General Data Protection Regulation, GDPR, which sets rules about data bases collected about people. That also gives any individual the right to ask whether there's any information about them collected, what said information is used for and within reason have the option to ask for the information to be removed or otherwise deactivated.
Agreed, a list of nicknames is not a cross-linked database so that you could find other information about them but it's a start. Also agreed, the very same nicknames can be picked one by one by scrolling through all of the millions of posts from tens of thousands posters starting from day one. By hand that would be a mission impossible as it would take ages to load the pages and copy-paste the names into and Excel table. Most likely one could coad a bot to do the hard work a bit faster and even check the profiles and add that information for each and every one. That would already create a cross linked database where you could sort the names by e.g. gender, age, joining date, location, certain social media users... And the links to their social media or websites can reveal even more information about them including real name, address, phone number, family and pets, car registry plate... All of which can then be combined to a reliable looking package for stealing one's identity!
So a list of names could provide a jump start for an evil data miner and that's why it's not public.