Key word is modern. Modern play is not barebones and the DMG doesn't help at all.
It's not that WOTC don't know how to do it. It just wasn't the point.
Again. The explosion of popularity of 5e was not expected. The 5th edition core books and strater sets were written for people who already play D&D.
5e wasn't designed to teach new DMs. It was designed to teach 5e to old DMs.
5e was designed for
- 1 veteran DM who left D&D in 2nd, 3rd, or 4th edition
- 2-3 D&D fans
- 1-2 newbies who would have "Human Champion Fighter" thrown at them
The assumption was that your DM already knew how to DM. Because the DMG didn't teach you know to DM. It taught you how to convert your old settings to 5e.