Diesel engines why not more available in smaller vehicles ?

Our diesel SUV has a 2.1 liter straight four, 200 hp, 369 ft-lbs. It drives beautifully. Averages 33 mpg around town, 35 on trips and will pull 40 on flat constant speed freeway. Not bad for a 4,300 lb vehicle. It is quiet, quick, smoke and smell free. By the way, Mercedes priced it $500 less than the equivalent gas counterpart. I save about a thousand dollars per year in fuel costs over the gas model. Not chump change.