But why isn't it? Why not have the first half full of not only teaching how to play the game, but different playable scenarios that build in complexity. A new DM could dive right into the first one, while a veteran would have a bunch of handy plug'n'play adventures ready to insert as desired. Then focus the back half on optional rules, yes, but fully developed ones. Right now, to actually use any of the optional rules in the DMG you have to go to another source where someone has put in the effort to figure out how to make them work in a useful way.
Put the magic items in the PHB with the rest of the equipment.