As has been said on here lorra lorra times before - the more complicated these systems are (any brand), the more there is to go wrong.
DPF/EGR - what a great idea for pollution controls but replacing them every 40,000 (_?_) miles just pushes the pollution elsewhere - mining/manufacturing/shipping etc. Also fuel economy goes down - so end up just swapping a couple of pollution items for other types of pollution.
Still - gotta keep the consumer consuming.
Ok - maybe a little exaggeration but I'm sure on these forums there have been problems at 20,000 odd miles and some haven't had a problem in 100,000+ miles. Pros cons etcetc