Not easy to get through all the EPA regulations. Look at ALL the small to mid-sized diesels offered in other countries--and not just in pickups. Only VW has put the effort into jumping through the US EPA hoops to sell their TDI here.
We just have to convince the automakers that it's worth the effort to play with out government and that there's a market for the vehicles they already produce--but just don't currently sell here.
Jeep did it with their Liberty, but only 2005-2006, and discontinued it in 2007 due to emissions regulations. Maine, Vermont, Massachusetts, New York, and California had already banned sale of the vehicle due to their rigid state emissions regulations.
Jeep had a Mercedes-Benz diesel available in their 2007-2008 Grand Cherokee.
"In North America and elsewhere this 3.0 CRD V6 was available from 2007, but was short lived. The Mercedes-Benz sourced unit meets stringent Euro 4 Emission standards
without the need for a diesel particulate filter
- which hampers vehicle efficiency, however - it includes a diesel particulate filter (North America only) to apparently further reduce exhaust emissions. It was not however available for sale in California
or certain Northeast states, due to new stricter emissions regulations for non-commercial vehicles. Vehicles could be bought used in California and Northeast states, as the regulations only applied to new vehicles."