See "What's the relationship between YC and HN?" in https://news.ycombinator.com/newsfaq.html YC existed first, then 'news' was added as experiment and the domain kept. Afaik users don't mind. It's just a name. Some more background at https://en.wikipedia.org/wiki/Hacker_News

It was originally called "Startup News". Putting it at news.ycombinator.com was a smart move because it prevented any confusion arising when changing its name to "Hacker News".

Actually you should add in https://news.ycombinator.com/newsguidelines.html Link to https://news.ycombinator.com/newsfaq.html that answers the question

Little known domain hacker.news exists but it redirects to the ycombinator domain