Not true. The purpose of a rulebook is to teach new players how to play the game. And for new players "just build as much as you need for the adventure" is the correct advice.
Elaborate Tolkienesque worldbuilding is a fun activity for some, but it's a different activity to playing a game of D&D.
Don't forget that "new players" may include people who are new to D&D but not RPGs in general, people who are new to DMing but not to D&D, people who are new to building a setting but not D&D, and people who are seasoned worldbuilders but not used to worldbuilding for D&D.
And
especially don't forget that there are two parts to D&D that can hamper "build just as much as you need": The game's lore and the player's character ideas. You can start out with just your version of the village of Homlett and just enough of the surrounding areas for you to get the PCs to the next tier of play, and then one of your players wants to play someone from a far-away city or another continent or even another plane, or something else that has heavy lore attached to it. You have your tiny village of mostly humans and a few Tolkienesque species, and the party consists of a warforged, a plasmoid, two drow, and a gith. Whoops. That "build just as much as you need" didn't cover
that.
So "build just as much as you need" is correct advice, but not the
only correct advice. (And "do you want to limit the species the PCs can choose from, or can they pick anything they want?"
is a worldbuilding question.)
Now, this hypothetical DMG
could include advice on group worldbuilding activities, or on getting the players to build the lore and the world as they go along, PbtA/DungeonWorld-style, in which case "build just as much as you need" is perfect. But these rules would also have to emphasize that it's OK for players to create the lore--which has been a big bone of contention on another thread in which I'm engaged in pointless arguing re: backgrounds, with some people treating letting players make up stuff like this as totally anathema to them.
Also, top-down worldbuilding--which doesn't have to be Tolkienesque in its depth--does have many benefits. It helps with consistency and the setting's tone, which is great. Greyhawk may be much loved by some, but not everyone wants a game that's low medieval fantasy except there's a crashed spaceship. Or they may want a game that's low medieval fantasy
and has a crashed spaceship
and that spaceship has had wide-reaching effects on the entire region, if not the world.