The book also says it is a set "guidelines" meant to be tweaked for whoever, however. The group will work however it works. If you had certain expectations of things being by the book, I recommend asking the DM how the campaign will be in order to form reasonable expectations. I'm being facetious in repeating previous arguments, but I do believe this to be true.As for Oofta's quote, he is correct. It says it right there in the DM's Guide, in the opening pages no less. That doesn't mean that players are exempt from helping. It says it is the DM's job. It is their creation.
And "it is their creation" is half correct. What is "it?" The setting alone? The whole campaign? The DM brings the most to the table, but unless they made the Player's backstories and character traits, then it is not all theirs. Minute changes still matter here. Is this minor? Yes, but "it's MY world" has been said on this threat more than once so it's necessary to point out again.