First, who said anything about less of what you don't like? The book can be made bigger. The current DMG is only like 320 pages. The Level Up Adventurer's Guide, conversely, is twice that size and is probably as big as you want a dead tree book to get (any larger and they come with the threat of a hernia), which leaves plenty of room for actual DM advice and expanded worldbuilding advice and optional rules. And a pdf or online source like DDB can be even larger. While I enjoy actual physical books as much as the next person, well, my eyes like it when I enlarge the text on a pdf. Plus, well, pdfs are are usually cheaper than physical books, which my wallet appreciates, and can also be more easily errata'd as well.
Secondly, the point is to make sure that this knowledge actually accessible. A new DM isn't that likely to know about those sites. There are probably dozens of GM advice sites I've never heard of, and I've been gaming for decades.
Thirdly, people shouldn't have to buy the DMG and one or more starter sets just to get information that should have already been in the DMG.