That's a result of Tokyo and the other biggest cities only separating into recyclable bottles, non-recyclable or non-burnable material (i.e. inorganics) and all the rest which is as you say incinerated.

They also have some, if not the most clean burning incenerators in the world, and they use the waste material for construction and land reclamation.

Burning plastics at very high temperatures is far more environmentally friendly than sending them to landfills or attempting to recycle them.

Nevertheless they are known for excess packaging and obviously my arguments about standardization still apply to Japan as much as anyone else.