big factor is low quality fuel. used to be a big issue here until govt made it illegal to have smoky vehicles, so fuel companies had up their game.
navaras have been heavily influenced by the euro market (which is why navara have so many 2.5 litre engines not 3 litres) where they tend to have good fuel.
the other thing is servicing. lack of resetting the fuel data when doing fuel filter changes means it over-fuels a fair bit until ecu learns the change. part of that is simply clogged up fuel filters due to poor quality fuel.
and then knuckle draggers who think a smoky diesel is a good diesel.