Sometimes sub-categories become so big and so popular that they overshadow the original category they were originally derived from.
A search engine is an information retrieval system designed to help find information stored on a computer system while a Web search engine is a search engine designed to search for information on the World Wide Web. (source: Wikipedia)
Today, a search engine is a web search engine. The sub-category overtook the main category.
Jiu Jitsu (or jujutsu) is a martial art from Japanese origins. It landed in South America in a Judo like form and the local practitioners created their own brand of this grappling system that became known as the Gracie Jiu Jitsu.
The Gracies made a marketing mistake by patenting trademarking the name (but that’s another story) of the category and the art became Brazilian Jiu Jitsu.
Today Brazilian Jiu Jitsu simply became Jiu Jitsu and overtook the original category in popularity to the extent that the original is now referred to as Japanese Jiu Jitsu!
The observation to make from these two examples is that the sub-categories did not change. Web search engine companies did not become computer search engines nor did Brazilian Jiu Jitsu practitioners delved into the Japanese form.
The sub-categories simply became more popular than the categories they diverged from overshadowing them to the point of taking over their names.
