The diesel engine is by its nature bulkier, heavier, more complex - thus more expensive. Regarding "small passenger cars", costs are an important argument. Thus I guess this is the main reason for a lack of diesel offers in small passenger cars.

Regarding "polluants" it depends on what exactly you consider a polluant: diesel engines tend to create more NOx (due to higher combustion temperatures), and soot (absent in petrol engines if not of the 'direct injection' kind). And slightly more CO2 (as diesel has a slightly lower content in hydrogen than petrol).

Hope this helps

In small passenger cars the petrol engine is favored over the diesel engine because in the start speed ,  the petrol engine is faster than the diesel engine specially in medial east. 

Without emission control, petrol engines emit more CO and HC, similar NOx, and lower particulate emissions.

With emissions controls, differences between emissions are much smaller, though NOx and particulate emissions are much more difficult to reduce in a diesel than in a petrol engine using a 3-way catalyst.

The diesel engine will have about 10-20% lower CO2 emissions.

Diesel fuel weighs 850g/L, petrol weighs 750g/L. Hence diesel yields more km/liter than petrol becasue it is about 12% denser than than petrol.

Considering the holistic cost of ownership for small passenger cars. petrol ones are cheaper for lower mileage drivers doing shorter trips, diesel ones are cheaper for higher mileage drivers doing longer trips. 

There is the general perception that petrol engines are more responsive and hence more desireable to drive, although those perceptions have been changed in recent years by improved diesel engine technology.