There is. But Chevy and Ford threw a GIANT fit about it. They didn’t want to do a full redesign of their blocks and heads until 2025. (This was back in 2015). They sent reps to the EPA board and through a crybaby fit. They couldn’t get the NOX or Carbon emissions down without that filter in their designs then, which are largely unchanged internally since 2015. Meanwhile, the Cummins 6.7 meet 2030 emission standards in place at the time without DPF. When Cummins started the 6.7 design in 2006, they spent tons of time and money on R&D because the PM at Cummins and Dodge did not want that damn setup on their trucks. Too expensive and too risky. So they over designed and focused all efforts to reducing the emissions through complex injection timing and turbo boost. The intakes were designed to be as equal as possible, smooth as possible and the turbos were given variable vanes to adjust. They damn near came close in the 5.9 to meeting the emissions of 2030, I mean right on the edge. So they felt they had tuned the max out of that, so they enlarged the bore. This helped with exhausting the heads and boom, emissions were met and exceeded the standard.
The problem is, Ford and Chevy had already completed their redesign cycles BEFORE the revised emission laws came out and were caught flat footed. So the DPF came about as essentially a bolt on option. They were so bad on emissions, that Chevy had to start in early 2008 using the DPF and Ford a year later. It wasn’t until 2016 when the EPA forced ALL Diesel engines in the use to have a DPF regardless of emission numbers that Cummins finally broke down and had to put one on.