To expand on Brain’s answer…
StackOverflow and later all the other StackExchange sites were create to enable. “long tail searches” when a person searches for the problem they have on Google and are then taken straight to the questions/answer about that problem without having to use the rest of the site; Google is our home page.
How we arrange the site is not important to the people we are trying to reach, tagging etc is mostly there to help the people that answers the questions . We need more “normal” users to read answers that help them and ask new questions – we already have enough experts to answer the questions!
Likewise is it not important if the site gets awfully cluttered provided it still gets lots of traffic from Google – StackOverflow is one of the most cluttered and poorly organized sites I have seen, however it solves a lot of people’s problems, so keeps growing.
Therefore we need questions that rank at the top of the Google results for a person’s search. Also a Google user gives great weight to the page title when deciding on the search result(s) to click on.
So a question with a title of “Rules for taking bakes on the London Tube” is much more likely to be read by a Google user then a questions about “Rules for taking bakes on mass transit systems”. (The fact that an English person will not use works like “mass transit” in the search make this even more so.)