If Simon Reese knew about the Axis Mundi and song why did he wait until it was to late to tell Alex

I never got why Simon wouldn't help Alex more. He seemed to know so much and apparently wanted to stop the Demon Uprising but yet he would never tell Alex what she really needed to know until it was too late i.e. the playing of the songs in succession to end the world. To me Simon would have had a better chance stopping everyone if he would have helped Alex.