Because, if your newsserver restricts access to a certain group, you can just as easily connect to another server that has what you are looking for. A newsgroup can be hosted on servers that are outside the Internet and a lot of them are. To search for special topics is relatively easy even for newcomers. Newsgroups in those eight categories are created by an approval process, which includes formal discussion and voting. In the alt.
Some groups focus on special topics with limited distribution.
Most newsgroups are unmoderated. They let you search for newsgroups that deal with a special topic, or for specific articles about your subject of interest, or in a selected newsgroup. You can search for new or archived articles, and in the newsgroups you can publish your opinion and ask questions. To participate in newsgroups, you should learn the purpose and the norms of the newsgroup before posting any articles of your own. A good rule of thumb is to read articles for two weeks before posting, and then follow the norms.