The main reason is to make sure that no knowledge is lost throughout generations.

If you want to contribute, please take into account the namespace in which a page is located in. This is important because the namespace controls who can see and edit what. Some pages are meant for everyone in the whole wide world and some pages are only meant to be seen by a select set of eyes.

To learn more about the technicals, the DokuWiki documentation is a good start, especially the page on syntax, if you want to start writing something for the wiki.