'it might be to do with them wanting SD to cater for large parcels too with DHL now being brought on board SOON but they have / had  nothing to lose by allowing custom for those parcels until they do so I don’t get it.' 

Perhaps the thinking was if they let people happily carry on using Custom for large parcels, to then be forced to use SD for large parcels, would annoy everyone all over again...

When they finally roll out large parcels with Simple Delivery/DHL, they might even think we will be grateful.... 😂