You can write articles on different topics at HubPages. Many do that. An article at HubPages has its merits on the on the article itself. In other words, it stands alone regard being found on an internet search for a topic by a user.
A niche has importance with blogs and websites. In that case many articles on the niche contribute to the blog or website itself being found on an internet search for a topic by user. In that case the more articles on a topic on the niche topic gives more value.
A HubPages account is "NOT" a blog or website. It is an opportunity to write and publish articles.
For more on HubPages go to the FAQ and the Learning Center. You can discover links to those at the 'Help' queue at the upper right of a page.