Mistwell
Crusty Old Meatwad
Uh, I would, except that no one has that expectation. The PHB contains the rules of the game, and it's a pretty hefty tome. The DMG was supposed to be where we would be getting the rules for the other modules that would make the game run like some of us are interested in. We have a few pages like that, it's true, but nowhere near the actual rules pages.
Count again. The actual rules of the game in the PHB take up fewer pages than the Optional Modules sections of the DMG just from the index, and that's not counting any possible sidebars that provide Optional Modules outside that section of the DMG. I think you're looking at the PHB size overall without considering how much of it is devoted to stuff like spells. But rules? DMG already says it's going to exceed the number of actual rules pages found in the PHB.