Webmasters sometimes move web sites from one domain to another, change the URL structures pointing to their web pages, or rename those pages themselves.
Changing the URLs for pages isn’t something that should be done without a lot of thought, and without very good reasons. Especially if there are many links and references on the Web to the old URLs. See Cool URIs don’t change for a number of technical ideas on planning what to use for your URLs so that it’s less likely that you might need to change them.
Regardless, webmasters do sometimes change the URLs for pages found on the Web.
This can sometimes happen when the owner of a site decides to change its name, or to rebrand its products, or merges or acquires another site or business and wants to consolidate the web pages from the other site under one name. It can also happen when a blogger decides to change the permalink structure of their URLs. Sometimes product lines are renamed, and the sellers of those products want people looking for them to find the products under the new names. There are many other reasons why the URLs to pages change.