This is one of the biggest hand-waves in the whole concept - "All Myths Are True", but everything is essentially the same as it is in the "real world". This is probably largly due to an effort on the designers' part not to reduce, trivialize, or offend existing religions, and partly because everyone has their own idea of how things would have worked, and so having an official world wasn't worth the effort.
Oddly, what almost works better, is 1st edition's premise that the old Gods have been away, and are just coming back again. Then history can be as it is until now,...