

Large populations tend to have a lot of shared utility and a lower per capita emissions standard as a result. Countries with lots of mass transit and dense housing enjoy significant efficiences of scale. One reason why India looks so good on paper, despite having some abhorrent ecological policies in practice.
Smaller countries - especially small tourist countries - tend to have emissions far higher than their native population size would suggest. Places like Qatar, the UAE, and Kuwait regionally top the emissions per capita chart as a result. Canada and Russia also score badly in no small part because of how spread out the population ends up in countries with enormous amounts of wilderness.






It has too many people to avoid the economics of scale that blunt per-capita emissions rates.
As the number of people using a public service increase, the per-capita waste declines. A bus takes roughly the same amount of gasoline to move 5 people as 50. Cooling an apartment block during a heat wave is more efficient than cooling an equivalent number of stand-alone houses. And as the apartment approaches 100% occupancy, the net benefit is spread over more people. Industrial scale refrigerators consume less energy overall than individual freezers.
The more people using a piece of capital, the less energy is wasted through its continuous operation.