My take on it, is that Honda felt the need to provide a diesel in some of their models in order to maintain market share in Europe (as well as the Accord, the engine is available in the Civic)
Unfortunately (I say that based on hindsight), the diesel was being pushed in Europe because of its better mpg compared with petrol. To facilitate this, VED (Vehicle Excise Duty aka yearly car tax) became relative to the CO2 emissions i.e. the lower the CO2, the lower the VED. Small cars with small petrol engines (1.0 litre) compare on CO2 levels, with large cars with large diesel engines. So if one wanted a large car with low VED, one would be inclined to purchase a diesel variant. Plus, because they have turbos, they can be remapped more easily.
However, Japan had decided a long time ago that diesel was bad, so there are hardly any diesel cars in Japan (as in the USA).
To create a diesel engine, the Japanese manufacturers just copy the Germans e.g. the Honda diesel engine is a Honda block/head, cylinders/pistons, and manifolds, but the rest is basically Bosch, including the engine ECU. Indeed, I'm not sure how much of the block/head & cylinders/pistons is not an off-the-shelf design.
If one wants good mpg, a diesel will always beat a petrol hands down, because one of the things that affects the efficiency of any IC engine is compression ratio - the higher the compression ratio, the more efficient the IC engine. You can only take the compression ratio so far on a petrol engine, after which it tends to auto-ignite and effectively becomes a diesel, but since the fuel arrives too soon in the cylinder and the pistons and cylinders are lighter in a petrol engine, it will not last very long during auto-ignition. Also, it is much easier to add a turbo to a diesel and increase efficiency further, this is because the diesel requires no butterfly throttle in the intake i.e. a diesel's inlet is wide open all the time - hence it runs lean, which is actually its achiles heel, because lean-burn is the cause of NOx.
The diesel vs petrol debate on car forums is infamous. Petrol-heads hate diesels. I have never owned a diesel car, my Accord is the CM2 which is 7th gen with a 2.4 petrol engine (I have a few other petrol cars too), but the 2.4 petrol struggles to get over 30 mpg, whereas 30 mpg on the 2.2 diesel would indicate a problem. Whilst I never hated diesels in cars, I am beginning to think that they have just become a German scourge LOL
Regarding the DPF, it's a last-ditch sticking plaster to clean the engine up. But due to the VW scandal (AFAIK it was a Bosch ECU and it always had the code for testing purposes, but VW R&D deliberately kept the code enabled) .... RIP the diesel LOL