Quote:Because there is no authoritative set of rules for English.
Style guides set forth their authors' views of the rules of the English language. Most people learn the rules before sitting down at the wheel of a car, or sitting behind a gamemaster's screen; why should sitting in front of a typewriter be any different?
Some of the rules in style guides are either debatable, or wrong. They state rules as absolutes when, even in the best written English, some are only trends. They fail to list all the exceptions, and there are some issues they do not address at all.
A style guide can be useful, of course - most of what they say is the undisputed truth - but they should not be used uncritically.