That's because those the countries importing them make that proposition economical.

For the Chinese, producing a car is like producing a hammer: only the production costs count.

Driving a polluting car in China seems to be getting more expensive. That's why they do it less.

Driving a polluting car in, say, the US, is not getting more expensive, so they import those cars.

The air quality in other countries doesn't effect them as much.

First, air moves, so that is not totally correct.

Second, the local air quality is related to local policy: if other countries want to improve their local air quality, local policies are needed.

China seems to be working in that direction, although they are by far not yet there.

They are also exporting more electric vehicles than ever before.