In this article, the author discusses the idea that “cool URLs don’t change” and how this belief is often proven false in practice. They provide examples of instances where cool URLs may not change, but become inaccessible to the general Internet and even to logged in users. The author highlights the cases of Reddit and Twitter, where protests and changes in corporate policies have led to restricted access to content. They note that while some websites have always required registration for access, the long-standing openness of sites like Twitter and Reddit has resulted in numerous references and links that are now relatively inaccessible. The author also mentions the incentives for open websites to keep their URLs stable, as it encourages linking and drives traffic. They conclude with a reminder that there are various reasons why individuals may choose not to register on a website, such as agreeing to unfavorable terms of service.
https://utcc.utoronto.ca/~cks/space/blog/web/CoolUrlsGoInaccessible