A toy that does one thing gets played with until the child has seen it do that thing. Usually about four minutes, spread over a fortnight.
A toy that does nothing gets played with for years, because the child has to supply the idea, and the idea keeps changing.
That's the whole argument for open-ended play, and it's not really about wood versus plastic. It's about who is doing the work.
What "open-ended" means in practice
Something with no correct outcome. A set of wooden arches is a tower at ten months, a tunnel for a toy car at two, a bridge at three, and a fence around a farm at four. Nothing about the object changed.
Compare that with a toy that lights up when a button is pressed. The child presses it. The toy responds. The transaction completes, and there's nowhere further to go — the toy has already had the idea.
The categories that keep working
Things that stack and nest. The longest-serving toys in most houses. They start as objects to knock over, become objects to balance, and end up as props in something else entirely.
Things with a mechanism. Gears, beads on a wire, a maze to trace, a latch. The appeal is cause and effect that the child causes — which is why a wooden busy cube outlasts a battery toy that makes a noise on its own.
Miniature versions of real things. Wooden pots, pans and kitchen tools. This is pretend play, and it arrives around eighteen months to two years — before that a wooden spoon is a wooden spoon, which is also fine.
Soft things with no instructions. A plush animal is as open-ended as anything gets. It's a passenger, a patient, a pupil and a pillow, depending on the week.
Where the plainness helps
Detail closes options. A wooden car in a single colour can be any car. A licensed character car is that character's car, and can only ever be in that story.
The same is true of faces. A stitched, neutral expression can be happy or sad depending on what the child needs it to be. A moulded grin is permanently delighted, which is no use when the game is that someone is poorly.
The honest limit
Open-ended toys are less impressive on the day. They don't demo well, they don't make a noise in the box, and a two-year-old opening one will often go back to the packaging.
They're also not a moral position. Children like flashing lights. Nothing is ruined by owning some.
The claim is narrower and more practical: if you want a toy that's still in use in three years, buy the one that does less. The child fills the gap, and the filling is the play.