Hello! You can read about Wikipedia's guidelines on linking to fan sites here: WP:ELNO. Specifically this part:
Do not add external links from: "11. Blogs, personal web pages and most fansites (negative ones included), except those written by a recognized authority.
And you are correct, that these links are on other articles means they should be removed as well. Wikipedia is a work in progress and things that go against the guidelines and policies can go unobserved for years or longer. SQGibbon (talk) 05:28, 16 November 2021 (UTC)