I am quite certain that if you were to open up a book that was either an instructional manual or reference manual for any other hobby - much less any other human endeavour - there would be relevant subject matter examples. What's more, I am quite certain that any such manual would be almost-universally reckoned as badly written if it lacked them.
It's not as if other hobbies - or other things you can do as a hobby - are less open-ended than being a DM when it comes to creative expression writ large (even if some might be); nor are they practiced by people who lack the faculties to be DMs.
So suffice to say I find it perplexing that anyone would willfully argue against relevant subject matter examples in the DMG - for instance, subject matter examples on how to adjudicate situations in gameplay - and I don't find the arguments against presented thus far compelling. Such arguments seem to rest on the assumption that "being a DM" is a hobby that is sufficiently distinct from others that the reference manual for DMs somehow ought not to be written and organised in a manner comparable to a reference manual in literally every other hobby or activity that can be done as a hobby in the world.
All that is to say nothing of the fact that the DMG already has, without any apparent widespread controversy:
(a) how-to examples of doing DM stuff (creating a new subrace or race, both of which have fleshed-out examples, and creating a new background, which describes an example background in each step of the suggested process)
(b) example/fixed DCs for several adventuring tasks - foraging, tracking, and social interaction. However niche the first two might be in many games, the last is, strictly speaking, at the heart of what is ostensibly one of the pillars of gameplay!
(I wouldn't be surprised if there is more along this vein, but I don't care to flip through the DMG to find it.)
Now I come to think of it, it's also to say nothing of the fact that the PHB is for the most part written and structured in the way you would expect a reference manual for a hobby to be written and structured. To pick an example at random:
The section on ideals doesn't include any example ideals in and of itself - but that's all right, since every single background in the PHB includes example ideals, and the rule section on ideals refers to those ideals. What's more, that rule section does include examples of/guidance on what to think of to come up with an ideal: "Ideals might answer any of these questions: What are the principles that you will never betray? What would prompt you to make sacrifices? What drives you to act and guides your goals and ambitions? What is the single most important thing you strive for?"
