Its simple in my mind, COST, £300-£400 for an egr/dpf delete compared to £1800 for a dpf/CAT for a 2.5 year old Corsa where dealership refused to replace it for the 2nd time under warranty laying blame on customers driving cycles.

Not an excuse in my opinion as the car obviously wasn't fit for purpose.

If aftermarket dpf's fail to work (which from what you read is common) then either a cleaning route is taken which again isn't a guarantee then what other choices or options other than genune DPF which can often write a car off.