alt Hacker NewsOf course, but mostly it's just recirculation that causes costly engine rebuilds. If it wasn't so expensive no one would delete.
Most regulations target emissions at point of sale but don't give a toss if such systems are practical or maintainable. It's sometimes better for the environment to have more emissions but not so much waste from having to buy a new thing more frequently.
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No the DEF systems tend to break down and its mandated the engine go into limp mode when they do, this is hated by those that do not care for emissions and one of the biggest reason to delete by truckers. Also costly to fix the systems out of warranty.
You can find instructions on how to make DEF simulators using raspi's to fool the ECU into think the DEF system is working, people who do care about emissions will still carry these for emergency so they continue on their trip and get to a shop later. The derate was over zealous for sure and was a bad policy.
Also DPF is a performance issue since it blocks the exhaust to some degree, same with catalytic converter with def nozzle so no its not just EGR at all. DPF also consumes more fuel for regens.
2027 diesel regulations was to mandate even more NOx control but also specified manufacturers were required to have 100,000 mile 10 year warranty on emissions systems, its 5 year, 50k now. I believe thats dead in the water now.
A diesel engine with a deleted SCR system puts out 40 times the NOx of a working one. Thats 40 trucks going down the road to 1 equivalent. NOx causes asthma and acid rain, its not for the environment as much as for you directly.
I've got a 2011 BMW X5 diesel with 189k miles on it. The DPF went out at around 150k, which is roughly the expected lifetime from my understanding. The part alone is ~$4000. Regardless of living in CA, I'd have replaced it anyway because I think it's the right thing to do. (I didn't want a non-DPF diesel that was emitting lots of PM2.5s when I made my purchase).
That said, many people would prefer the money in their bank account. And if I had decided to sell it rather than fix, no doubt it would have gone to someone looking to delete the DPF.