Delivery charges
I worked for DHL before the Germans took them over. Whilst we had the volume/scale that Sprogs rightly talks about, we hated domestic delivery of anything which had to be signed for - and signed-for deliveries is what we did!!. At most people wanted to pay £5 to £10 for a domestic delivery. Each and every one of those deliveries cost us over £15 back in 2002. If we could avoid domestics, we did.
I have no idea how anyone expects to make money on domestic delivery, other than the post office.
The customer doesn't want to pay and the selling company doesn't want to pay.