Those of us who have been using the internet for a reasonable time used to spend time posting in newsgroups, using a system called “usenet”. This article suggests that usenet’s decline was due to the sudden ease with which it became possible to search the archives:
Usenet is a medium not too dissimilar to many blogs today, where people wrote informally. The half-life of a Usenet posting was several weeks - it depended on the popularity of the newsgroup - but in most cases archives were not maintained, or easily accessible. And Usenet continued in rude good health long after its demise was predicted. Then, Google took over the creaking archive from Deja, and made searching the entire historical record trivially easy. People simply stopped using it. Usenet died the day Google turned it into a database.
It’s a cute theory, but it’s entirely wrong. No one ever thought that usenet posting would disappear forever - or at least only the naive and uninitiated did. Usenet was really killed by two other things: ISPs stopped providing access to it, and PHP - an awful technology, of course, but very useful - made it trivially easy to set up a discussion group based on a web page, rather than on some more technologically limited system. Websites like slashdot, weblogs with comments and the near-ubiquitous php-driven discussion forums are the true successors to usenet.
Coincidentally, the rise of php was at about the same as Google bought the usenet archives, but as one is constantly reminding students of history, just because events happen in a sequence does not mean that there is a causal link.