You can perform a whois search to see if and when a domain got registred.
helloneighbor.com is taken since 2002 and gunpoint.com since 1996. The names were not available for the games which came much later, so they had to be creative in their domain choices.
When it comes to domain names, short and generic is usually better than long and specific. But if the name of your game is already taken, attaching "game" is the next best pick for search engine optimization. When someone wants information about the game from Tiny Build and Dynamic Pixels, searches for "hello neighbor" and the first hit is an air freshener, they will try "hello neighbor game" next. If your search query is already almost a domain name, then most search engines will usually rank that domain first, even if other websites rank higher on the search terms when it comes to content and inbound links.
By the way: The
.game TLD is available since May 2016. We will see if it will catch on. (Registration prices are far higher than for
.com domains, but for professional game development studios they are not prohibitively high).