This.
Plus, it can be slow. I had a parcel from the UK take 9 days while just today I received a non-GSP parcel after 3 days.
Also, for international shipping the duties indeed are a bit arbitrary, while I suspect Evilbay to clear customs in bulk at a discount while charging the full amount to the buyer, and pocket the difference. Don't think for one minute this isn't earning them money.
It's a smart move to stimulate local sales platforms (which in due time can have their own price levels) and already earn some extra cash at the same time.